528 K. T. HILL — THE COMANCHE SERIES. 



Clear creek, upturned Packsaddle schists, with inclosures of the grauites. 

 The granites underlying the Potsdam and intrusive into the Packsaddle 

 schists were apparently of the same mass. 



Potato hill lies about a mile north of the Clear creek crossing and two 

 miles west of the escarpment. It is entirely composed of Potsdam sand- 

 stone, and its top is on a level with the crest of the adjacent escarpment. 

 Its strata dip gently toward the northwest. Conocephalltes tripunctatus (or 

 roemer'i), a fossil peculiar to the middle of the Potsdam series, occurs in its 

 topmost bed. At the foot of the escarpment, a little north of east of Potato 

 hill, Potsdam shales lie in contact with Burnet marbles. Toward the top 

 of the escarpment, fossils said by Professor Hill to be from the horizon of 

 the Trinity sands, the base of the 4,000 feet of Cretaceous strata, are quite 

 plentiful. These are about on the level of the Potsdam fossils not two miles 

 away. 



The contact of the Carboniferous with granites, which are overlain by 

 horizontal sandstones, and of the Potsdam sandstones and shales with Burnet 

 marbles at three different localities, suggest the presence of a system of 

 faults — vertical displacements — which must be taken into account while 

 considering the level of the central area when the Cretaceous was deposited. 



The injection of granitic material into the Packsaddle schists ; the clean, 

 fault-like contact of the " Shinbone " Carboniferous with the granites ; and 

 the apparent formation of the lower beds of the nearly horizontal strata of 

 the Potsdam from the decomposed constituents of the underlying granites, 

 all point out the post-Packsaddle and pre-Potsdam age of the latter. 



