Bulletin of Museum of Comparative Zoology 16-2 (1)

BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD COLLEGE, IN CAMBRIDGE VOL XVI (Geological Series, II.) I CAMBRIDGE, MASS., U S If: f' A 1888-1895 Reprinted with the permission of the original publisher KRAUS REPRINT CORPORATION New York 1967 r \, CONTENTS iv Page No 13 — Reports on the Dredn-ing Operations America to the Galapagos, the off the West Coast West Coast of Central of Mexico, and in the Gulf Alexander Agassiz, carried on by the U S " Commission Steamer Albatross," Lieut Commander Z L Tanner, of California, in charge of Fish U S N., commanding gos Islands No 14 — Contributions Museum Griswold (1 University L S No 15 V Report upon Rocks collected from the GalapaP Merrill July, 1893 By George 235 from the Petrographical Laboratory of the Harvard VI A Basic^Dike in the Connecticut Triassic By Plate.) 239 August, 1893 — Notes on^the Geology of, the Island of Cuba, based upon a Recon- noissance made April, 1895 for Alexander Agassiz By Robert T Hill (9 Plates.) 243 , No — Contributions from Harvard On the University the PetrograpMcal Laboratory of the Museum^ in Charge of J E Wolff PetrograpMcal Characters of a Dike of Diabase in Basin By William H Hobbs the Boston In the region north of Boston occurs a most interesting series of maswhich break through the slates and sandstones, and include sive rocks, quartz-porphyry, granite, quartzless-porphyry, elaeolite-syenite, diorite, They have been porphyrite, diabase, augite-porphyrite, and gabbro studied in greater or less detail by many observers, prominent among whom are W Crosby, M E Wadsworth, and J S Diller The rocks which have afforded material for the present study belong and may be seen in a series of exposures in Medford and Somerville They are coarsely crystalline rocks, and have borne the names "syenite "and "diorite." They have in general been careto a single dike, from similar rocks of fully distinguished finer texture known as " green- which were shown by Wadsworth in 1877 to have about the same composition as the coarser rock, and were considered by him as identical with it The finely crystalline rock seems to be more widely stones," distributed than the coai-se variety In the present paper it has been studied only at a few localities, where there was some promise of de- ciphering The its relations with the " diorite." age of these rocks has not been accurately determined, though they post-triassic on account of their lithologi- have generally been considered resemblance to the diabase of the Connecticut Valley The slates through which they have broken are probably identical with the Lower cal Cambrian argillite of Braintree Diller has furnished evidence to show that the finely crystalline diabase ("greenstone") is the youngest of the eruptives of this region, its dikes cutting those of the other rocks.^ Many mistakes have been made in determining the composition of " " both the so-called " diorite and " greenstone." The " diorite was long VOL XVI Bull — NO Mus Comp Zool at Harvard College, VII 179 BULLETIN OF THE ago described from the Granite Street locality in Somerville and S L Dana/ and by minerals feldspar and J W, Webster,^ as made up "by J This was supported by Professor hornblende The Hitchcock, in his Survey of Massachusetts.' mistake, which con- be hornblende, was farther repeated by Crosby.^ Professor "Wadsworth^ was the sisted in taking augite to Dodge ^ and W F essentially of the W W first to apply the microscope to the study of this region, and was enabled to determine correctly the general composition of tlie rocks His study included all the eruptives exposed in Somerville, and part of those out- He pointed out cropping in Medford, Maiden, Brighton, and Brookline the connection of the outcrops, and indicated their general trend He showed that the feldspar is plagioclase, and that the prevailing nonOn the basis of an observed identity feldspathic constituent is augite " in mineral composition he concluded that the fine-grained " greenstone " " is identical with the coarser Professor in his diorite." Crosby, Con- tributions to the Geology of Eastern Massachusetts,"'' has quite accurately outlined on his map the area in which these rocks are exposed The present article, being restricted mainly to the coarsely crystalline diabase, repeats to some extent the work of Professor Wadsworth "While the results are in the main confirmatory, there are still important points of difference, and some new facts have been determined Leaving out of consideration the vicinity of in Somerville, the field study has yielded but tlie Old Powder House The attempt has been mainly to add something to our knowledge of the petrographical characters of the so-called " Mesozoic diabase of the Atlantic border." Those who desire a full literature little of the subject treated in this paper should refer to the above-cited work of Professor Wadsworth Field Notes The dike of diabase which Street in Somerville to Spot although no examination '^ * ^ Memoirs Amer Acad., Boston Jour Pliil and is in the 1st series, Arts, here considered extends from Granite Pond in field IV Stoneham, and probably beyond, was carried beyond that point 16-3 (1818) XL 282 (1824) final Kep Geol of Massachusetts, 640-663 (1841) Proc Boston Soc Nat Hist., XVIL 415 (1875) Occasional Papers of Boston Soc Nat Hist., Vol III ^ Notes on the Petrography of Boston and Vicinity, by M E "Wadsworth Boston Soc Nat Hist., XIX 217 (1877) ^ Occasional Papers of Boston Soc Nat Hist., Vol III Proc MUSEUM OF COMPAKATIYE ZOOLOGY No outcrops of the coarse" rock have been found south of the Granite Professor Crosby has included the fine-grained diabase Street quarry "which crops out at the Pumping Station in Brighton, and similar rocks and Xewton, as a part of this dike ; but the great change of strike required, and the long intervening distance without exposures, From the Granite Street quarries to are opposed to the supposition in Brookline the Old Powder House in Somerville, (a distance of about one miles,) the strike of the exposures is N 25° "NV From and a half that point to In Medford and Somerville the Spot Pond, the trend is N 10° E Avhich has been thrown into gentle folds, the rock is argillite, country A notable exception to this statedips of which seldom exceed 35° is seen at the old slate quarry on Professor's Row, College Hill, where beds strike ±N 95° E and dip ±72° to the south The area ment of coarse diabase, which has an average width of about two thousand feet, The exposures of diabase alnever found in contact with the slate is most invariably show the well-known weathering to boulders in situ, though this is best observed at Pine Hill North of High Street in Medford the areal geology is complicated by the occurrence of granite and felsite, for the mapping of which very detailed field-work v^'ill be necessary The arrangement of exposures of coarse and fine grained diabase in the vicinity of the Old Powder House seems to show a gradual passing In the immediate vicinity of the Powder of one rock into the other House is an extensive outcrop of coarse rock, like that at the Granite and Pine Hill About four hundred feet northeast of the Street quarries Street the texture is much finer, though not be ranked with the normal " gi-eenstone." About six 20° W of the Powder House the rock is somewhat finer Powder House on Harvard sufficiently fine to hundred than feet S Again, at the corner of Elm and about one thousand feet west-southwest of the at the last-mentioned locality Morrison Streets, which is Powder House, the normal " greenstone " occurs in slate Moreover, on Willow Avenue, about fifteen hundred feet along the strike to the south from the Harvard Street line rock at locality, the From rock is practically identical with that seems probable that the coarsely crystalthe Powder House is near the middle of the dike, where the at the latter place this it cooling was slow, and that the gradual diminution in the size of the grains in going from that point is owing to more rapid cooling near the contact " The wide distribution of the " greenstone has made it impracticable for me to make a complete examination of it, but the few localities which BULLETIN OF THE have here been studied agree so well with each other, and with Professor Wadsworth's notes on the other localities where the same rock is exposed, that a complete study of with the " diorite." it seems unnecessary to prove its identity Petrographical Notes " observations that the so-called " diorite is " so-called the the rocks will be to greenstone," distinguished equivalent according to their mineral composition, without regard to coarseness of Having shown by texture or diorite field Microscopic examination shows the rock to be either a diabase The diabase is the principal rock, being found at the quar- on Granite Street (Nos 207, 209, 209 a, 214), and at the very exThe exposure on Harvard tensive quarries on Pine Hill (Xo 222) The diorite forms Street in Somerville is also of this rock (Xo 210) ries a facies of the diabase, and includes all the outcrops in the vicinity of the Old Powder House (Xos 208, 216, 218) except Xo 210, already mentioned as belonging to the diabase, and the hill north of High Aside from the Highland Avenue (Xo 203), the two rocks to be almost identical appear amphiboloid mineral, This rock is quite uniform in character, and occupies a large Diabase Street and east of — A macroscopic examination shows that it part of the area of the dike is composed mainly of a plagioclase feldspar, and an amphiboloid minThe proportions of these eral with more or less biotite and pyrite minerals vary considerably, causing the specific gravity to range from In weathering, the amphiboloid mineral is first de2.98 to 2.65 composed, causing a complete disintegration of the rock to a coarse feldspathic sand ination, and the The rock does not show the which have been feldspars, slightest evidence of lamlittle interfered with in crystallizing, illustrate well the divei-gent strahlig-kornig arrangement of Lossen, the remaining space being largely occupied by hypidiomorphous The feldspar grains are more or less lath-shaped ; of crystals of augite a white, pink, or green color ; generally striated ; and have an average length of about mm The specific gravity of cleavage pieces from Xo 222 was found to be 2.638 and 2.643 by determinations with the Thoulet solution, though these results are probably much affected by an In a single specimen (Xo 214), the cleavage of incipient alteration the amphiboloid mineral is so well developed that the mineral can be identified as augite in the hand specimen Under the microscope, feldspar and augite are found to be always MUSEUM OF COMPAEATIVE ZOOLOGY The present feldspar is shown by twinning striations to be plagioclase, In a number of fresh beautiful zonal phenomena which exhibits when sections the method of Professor Pumpelly ^ or M Michel Levy ^ was As is well known, this applied for the determination of this feldspar method consists simply in a determination of the and angle in the zone of the macro-pinacoid maximum extinction base, sections whicli are in this zone being characterized by symmetrical positions of extinction in Results the two sets of twins, with reference to the twinning plane were obtained as high as 27°, requiring the presence of a feldspar as In the classical work of Pumpelly above cited, basic as labradorite crystals of feldspar this from the Granite Street locality were determined by witli a modihcation of Des Cloiseaux's method method, combined for determining the size of the basal extinction angle sult obtained by the first method was 16°, The highest and by the second 3° re- to 4°, though, owing to the sections being inclined to the base, the latter rewere more or less unreliable He concluded that the feldspar was sults probably albite or oligoclase Mechanical separations of the constituent minerals have been made in In every case feldspar was a number of cases by the Thoulet solution removed with each separation between the specific gravity limits 2.76 and 2.6, and often a considerable portion came below the inferior limit The The and the wide range in specific be referred to decomposition products grains were found to be seldom pure, gravity is doubtless, in part, to was in several portion separated below the limit 2.6 careful washing to cases subjected ^ by both Boricky's and Behrens's^ methods, after remove all iodide of potassium Potassium as well to microchemical tests as calcium being always detected in this powder, that derived 222 was subjected 4.16% are from No chemical determination, which yielded The products of alteration of the feldspar to quantitative of oxide of potassium and a mineral which calcite, is probably kaolin Considerable often contained in the feldspar grains ; but it has apparently been derived from the biotite or augite by alteration, and has found the way to its present position in the feldspar throiigli green chloritedike material is the cleavage cracks This substance is the viridite of Professor Wadsworth, which he considered an incipient alteration of the feldspar Metasomatic Development of the Copper-bearing Rocks of Lake Superior Proc Am Acad., XIII 253 Mineralogie Micrographique, p 227 Archiv der Naturw Landesdurchforschung voa Bohmen, III Band, Abth., Prag, 1877 * Mikrocliemische Methoden zur Mineral Analyse, Amsterdam, 1881 BULLETIN OF THE From what now been seems certain that a feldspar as basic is attested both by the high extinction angles in the zone of oP and oo Poo as well as by the presence has said, as labradurite exists in the rock it This , That a feldspar of calcite as a significant product of alteration less and probably as acid, is present also, is shown by The potassium the zonal structure and wide range in specific gravity obtained from No 222 may be derived either from alteration products basic than oligoclase, 1) or from the feldspar which may be found in the (uiuscovite m ioto, The itself sequel, analysis of this rock shows by the small amount It therefore seems to of hydration that little alteration has taken place be certain that the potassium is derived from the feldspar itself, either from orthoclase or from a potiish plagioclase The principal non-feldspathic constituent broken up by feldspar is augite, which though rarely the feldspar is much is penetrated by augite, showing the nearly contemporaneous formation of the two The augite, which has generally a rose color, displays a faint minerals crystals, dichroism, the ray parallel to b being pink, and that parallel to a pinkBoth prismatic cleavages are generally well developeil, and ish yellow on the basal plane with the pyroxene angle 87° Parting parPoo and occasional twins according to the same plane, though not constant features, are observed in the rock from some localities Zonal structure is not uncommon, aud rarely the hour-glass structure is intersect allel to CO The principal alteration is to uralite, which is found in well developed rims completely surrounding many grains, while with others it has gone This farther, and found its way to the centre along the cleavage cracks mineral occurs in its usual form in scales or sheaves, and is easily dis- high double refraction, small extinction angle, and strong pleochroism, the ray vibrating parallel to the long axis being dark green, while that vibrating perpendicular to this direction is either tinguished by its It is probable that the uralite further changes green or bright yellow to chlorite but since biotite was generally to be found in the vicinity ; The distripassing into chlorite, it could not be definitely determined bution of the calcite shows that it is derived from the pseudomorphism of the augite, as well as from tlie decompositon of the feldspar Compact green and brown (basaltic) hornblende, though noticed once or twice, are extremely rare The biotite when tration of feldspar present and is generally either in plates, from its pene- augite, clearly original, or in fine scales or aggregate The former variety contains inclumasses in association with augite with the characteristic pleochroic zones too small to sions be determined, MUSEUM OF COMPARATIVE ZOOLOGY Both about them varieties have suffered alteration to the ordinary product, chlorite Wadsworth considered the biotite secondary to the augite, It an intermediate stage in the process of alteration that this more form of the much biotite, if seems, however, probable indeed secondary, is derived directly from the augite, and that the fur- Professor chlorite being ther alteration of biotite to chlorite sufficiently explains the occurrence The occurrence of biotite as a of the latter between biotite and augite pseudomorph after augite has been described by Blum,-^ Eichthofen,^ On chemical grounds, without Tschermak,^ Eohrbach,* and Brauns.^ assuming a high degree of metamorphism, the change from chlorite to In some sections, particularly Xo 207, a biotite is difficult to conceive large part of the chlorite can be referred to the diabantite of Hawes.® In many slides chlorite occurs in clearly defined hexagonal sections sur- rounded by one, or more frequently four or five, concentric rims of magIn other cases biotite can be seen in these basal sections in the netite act of changing to chlorite, the centre of the crystal being biotite, "which a wide or narrow rim of chlorite is tions No 202 and No 203, and shows the Figure is about taken from sec- different stages in this process of pseudomorphism Apatite is found as a constant constituent, in unusually large clear crystals, cutting all other minerals A present, which, in sorae cases at least, is netite, and ilmenite very small amount of quartz of secondary origin are present in varying amounts in hexagonal sections or more or less irregular masses Pyrite, is mag- Magnetite is either These masses are often elongated parallel to blades of chlorite, and are then evidence of Ilmesecondary origin A case of this kind is shown in Figure nite appears in sections, generally hexagonal, like the magnetite, but is In a section easily distinguished by its change to leucoxene or titanite from the Granite Street quarries (No 207) this change has been complete and the only vestiges of ilmenite are the masses of white, more or In other specimens (Nos 202, opaque, highly refracting leucoxene 208, 209 a) the decomposition has been less complete, but has taken place less in bands, which have three directions parallel to the sides of the rhom^ * * * Pseudomorpliosen, I Nachtrag, p 30; III Nachtrag, p 93 Wien Akad., XXVII 335 Blum, Pseudomorpliosen, III 96 Porphyrgesteine Oesterreichs, Wien, 1869 Min u petr Mitth., VII 27 Neues Jahrbudi, V Beilage Bd., 275 Mineralogy and Lithology of New Hampshire, p 120 BULLETIN OF THE This structure has been described (See Figure 2.) De and la Vallee Poussin and Eenard,^ observers figured by by many The structure has been explained by Teall as due to and by Teall.^ bohedral sectious intergrowths of magnetite and ilmenite, according to the fundamental rhombohedron Since the Gleitfldche of ilmenite is E, which is also the normal-solution plane,^ these may be due to decomposition along the From No 222 the heavy portion separated in normal-solution plane the Thoulet solution was subjected to treatment with the electro-magnet Material was thus obtained so magnetic that, when removed from the poles, the grains clung to each other like magnetized iron filings Treated with concentrated hydrochloric acid, this material was strongly attacked, but did not entirely dissolve even by continued digestion Wadsworth has described the occurrence of prehnite as a comThis mineral product of the alteration of the feldspar and augite occurs in veins at the Granite Street quarries, and to determine its characters a section was made from the mineral obtained from one of these veins The columnar crystals by macroscopic examination seem to have Professor mon their vertical axes, in general, perpendicular to the walls of the fissure long axis (c) always showed a sheafhaving perfect cleavage, both parallel and perThese sections afforded no interference pendicular to the vertical axis Another series of sections (basal) had nearly equal dimensions, figure In the slide, sections parallel to tlie like grouping of individuals with two equally perfect cleavages (» P) cutting each other at about 100° These sections gave also, in converging polarized light, a very perfect biaxial interference figure, with high positive double refraction and orthorhombic dispersion The optic angle when measured in air was found to be 83° 30', which is much smaller than the results obtained by localities The plane of the optic The prismatic cleavaxes bisects the obtuse angle between the cleavages age is very perfect, hardly less so tlian the basal No evidence of twinning Des Cloiseaux with prehnite from other by Des Cloiseaux* in some specimens, or that found by Professor Emerson^ in the prehnite of the Deerfield dike, was observed The only section of rock from the region under consideration in which like that noticed dites Memoires sur les Plutoniennes de Caracteres mineralogiques et stratigraphiqnes des Roches Me'm Couronpe's la Belgique et de I'Ardenne franfaise de I'Acad Roy de Belgique, XL 50, 74 Quart Journ Geol Society, XL 640 Cf Judd, On the Relations between the Solution Planes of Crystals and those of Secondary Twinning Min Mag., December, 1886 * Manuel de Mineralogie, p 430 Am Journ Sci., (1882,) XXIV 270 285 MUSEUM OF COMPARATIVE ZOOLOGY answer occnr in We have recorded evidence that similar terrace phenomena San Domingo, and the coasts Nicaragua, Yucatan, Jamaica, and in these regional uplifts of Pleistoof the Gulf coast of which the to recent cene and slight elevation time, of South America have participated the United States is In these studies I historj' (the insignificant have found no evidence that Cuba, since its earliest has had land connection with the United States Mesozoic) Unless there was some profound subsidence in Post-Tertiary time, such a as I have been unable to detect, no possible deduction can make such been has it that evidence In fact, I know of no positive connection connected with our continent at all, and have only hypothetical evidence that the Pre-Tertiary land may have once extended toward the Yucatan if ever, that the Antillean and peninsula, and that it was only then, can we avoid conceiving that Neither united were Cordilleran islands the subsequent elevations have brought the isthmian region up with it, tlie continents making the present land connection between The axial direction of the general Antillean Post-Tertiary elevation is and hence it is presumable that the subeast and west, approximately marine ridges wei-e more likely to have been extended in that direction, and that to the north and south of this axis, which must theoretically be the remnant of a great east and west swell or fold, there must have existed corresponding sloping sides and synclinal troughs natural, then, that evidence of the continuation of the It but is Cuban dias- in lines trophism must be looked for in east and west lines rather than north and south We can also reasonably conclude that the orogenic development of Cuba, begun in some unknown period of antiquity, was practically com- commencement of the ment accompanied by displacement, pleted at the Pleistocene, folding, — that is, and vulcanism, the developand that — the stage of elevation then began, bringing iip the old Pre-Pleistocene architecture and carving the mass into its terraces and present outlines The group of regional elevations which I have described, although marking a wide interval of time, all occurred in a comparatively recent To fix this time exactly would be impossible wuth the geologic period scant data at hand, but we can make some approximations The oldest of the elevations, now represented by the Yunqne level, certainly followed the period of folding wliich the Tertiary limestones underwent after their deposition This folding, we may safely say, was Post-Tertiary, and took place in late Pliocene or early Pleistocene time, approximately, and marks the beginning of the re-emergence of modern BULLETIN OF THE 286 Cuba, and the teiTaces are convenience we will all of later age Before this period, which for must early Pleistocene (properly late Tertiary) it be acknowledged that the area of Cuba, crests and coasts, was at least two thousand call feet lower in altitude than at present We cannot imagine that such a depression was locally limited to the island of Cuba or the Great Antilles, or that it would have abruptly terminated along the east and west axial line, and hence it is not difficult to infer, especially in the light of existing geologic evidence, that it involved the isthmian portion of the continent south of the great escarpment of the Mexican plateau, and that oceanic connection then existed between the Atlantic and the Pacific, as has been already indicated by the paleontology and by the living forms -^ ^ See A Agassiz, The Origin of the West India Fauna, Mem Mus Comp Zool., 1, p 79, 1883; also, Three Cruises of the "Blake," Bull Mus Comp Zool., Vol XIV., 1888 Vol X No MUSEUM OF COMPARATIVE ZOOLOGY 287 EXPLANATION OF THE PLATES PLATE Fig Fig I Geologic Section across the Island of Cuba from Havana to Batabano (2) Tertiary(1) Pre-Tertiary Formations Scale, inches to mile Limestones (3) Soboruco Reef (4) Mud Deposit of Batabanos Detail of Moro Plateau, North End of above Section Figures have same reference Fig Fig Dike near Water- Works, South Edge of Havana (1) Dike Material Cretaceous Clays weathered more The (-3) Supposed same, (2) (4) Surface showing Tertiary Limestone on right Geological Section of the Canon of the Rio Yumuri of Matanzas (1) Massive Coralline Cantera, Reef Rock, 85 feet (2) More Arenaceous Limestone, with Molluscan Remains, 15 feet (3) Stratified Calcareous Clay, with MoUuscan Remains, 10 feet (4) Same, with great number of small Pebbles (5) A very white Lime Material, with Bands of Clay (6) At Base (7) Calcareous Matrix, with Pebble, 10^ feet (8, 9, 10, 11) Mio- Fig cene Limestone with Molluscan Base (12) Remains, becoming arenaceous at (b) Elevated Reef Level (c) Military (a) Sea Level Hospital Level; {d) Cuchilla High Lands (1827), Yunque Level (e) Radiolarian Hill (2) Miocene {1) Limestone (3) Y'ellow (1) Soboruco Section at Baracoa ; ; ; Fig Fig Fig Clays with Miocene Mollusca (4) Hill of Radiolarian Earth Vertical height, tlie River Yumuri of the East eOO feet Section near Aguacate, showing Decay of Limestone into Red Residual The Canon and Terraces of Soil Ideal Illustration of the Epochs of Elevation in Cuba (1) Soboruco or Elevated Reef (3) The Cuchilla Level (2) Cliffs of the Coast (5) The Sierra Maestra (4) The Yunque Level PLATE The Evolution Figs 1, Figs 5, 6, II of the Circular Harbors of the North Coast of Cuba Mouths of simple Rivers, with Fringing Reefs growing off their Points (2) The Limones (1) The Y'umuri of tlie East The Development of the Circular Bay, by Erosion of the softer Material back of the harder Points of elevated Reef Rock (5 and 8, Mata Bay ; 6, Baracoa.) BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY 288 Fig Figs 3, Fig Note Example of Irregular Outline resulting from still more advanced Erosion (Harbor of Escondido.) Double-mouthed Harbors produced by Elevation of Barrier Reefs in combination with the Fringing Reef (3, Harbor of Jaragua; 4, Yamaniguey.) Matanzas Harbor, showing Yumuri Valley, Canon, and adjacent Levels — The artist has transposed the east and west sides in Figs PLATE III Limestone Mountains south of Matanzas PLATE IV Villa Clara, Metamorphic Mountains PLATE V Contact of Upland Plain with Limestone PLATE VL Typical Plain, Central Cuba PLATE VIL Yumuri River, Matanzas Bay PLATE VIII Yumuri Valley and High PLATE Yumuri IX River Levels Hills 3, 4, 5, 7, and R.T Cuba hill-Notes ok the Geoloov of _^,.^- •^M^SSML '^^^^^W^^^^I^^i^^ ,3SE:^:jr:i^:;^ T'-;':?*- (2) ??3i^^J0-^^^'