26 NORTH AMERICA/Continental Interior Figure (A) First and second order global cycles of relative change of sea level during Phanerozoic time (Adapted from (1989) GSA, The Geology of North America, v A.) (B) Sloss’ (1963) diagram of relation of sequences to craton Black areas are gaps (hiatuses) and white and stippled areas represent deposition of sediments during successive depositional episodes Note the stratigraphic section is more complete off the craton the sea incursions on the continent, so that the Tejas sequence is represented only by terrigenous sediments – material derived from the erosion of the newlyformed Rocky Mountains This is now the situation remains today – the interior of the continent is high and dry The end of each episode was marked by withdrawal of the seas and prolific erosion eradicating parts or all of the recorded history of the immediate and preceding chapters Several episodes of igneous intrusions into the sediments in the southern part of the Continental Interior took place during the later Cretaceous and Early Tertiary These small igneous bodies were intruded from the mantle at great depths rapidly along zones of weakness in the continental crust into the sedimentary section They are of interest, not only for their composition, time of emplacement, and implication for the tectonics, but because some of them, on