342 ' GEOLOGICAL SUEVEY OF THE TERRITORIES, 



22 feet, dark-gray shales, weathering a little lighter, containing Ostrea 



complexa and fragments of large Inocerami. 

 40 feet, of yellow shales, with white and yellow sandstones, full of Ostrea 



and Inoceramus. 

 17 feet, of light-yellow shales, of more marly character. 

 8 feet, of the same shale, traversed by plates of calcite from one fourth 



inch to one inch in thickness, of several feet in extent. 

 12 feet, brownish-gray shales, also with calcite. 

 40 feet, of gray shales, weathering lighter. 



120 feet, gray shales, partly dark, partly light, weathering rapidly, con- 

 taining toward their upper and lower limits pyrite and crystals of 

 selenite. 

 30 feet, of light-gray shales. 

 20 feet, of yellow shales. 



Above this there was rhyolite, having flowed from the southeast. 

 This thickness, of little over 300 feet, probably represents the average 

 thickness of the Cretaceous beds of that horizon throughout that valley, 

 as but small deviations from the general character were observed. In 

 going up to station 36, these same strata were found again ', but how they 

 connect I am unable to say. They certainly overlie the quartzite of that 

 station, dipping in a southwesterly direction toward the valley. Sec- 

 tion A, Plate XIY, will explain the relative position of the strata. It 

 runs almost due northeast to southwest from station 3G to station 35. 

 The trachyte (/) predominating on the western side of Coochetopa Creek 

 comes to a close there, and along the bed of the creek a coarse-grained 

 granite [d) crops out. Resting immediately upon it, we find a quartz- 

 itic white sandstone, (e,) covered by light shales -and shaly limestones;. 

 above these, another white sandstone; and then yellow shales with iso- 

 lated sandstone strata. These latter are the shales referred to in the 

 previous section, and it is they that are mainly covered by trachyte, 

 [g.) A few miles north of station 35 they are covered by drift, and do 

 not appear again until near the base of station 36. Whether the sand- 

 stone there is conformable or not with the Cretaceous strata, or what- 

 ever its stratigraphical conditions may be, could not be made out on 

 account of the utter lack of any ex^josure of structural conditions. The 

 next section (B) is taken through station 35 to station 88, having a 

 course of a few degrees east of north. Here the strata can be more 

 readily followed, and it can be made out with certainty that the sec- 

 ond sandstone stratum, (e,) probably even the first, bends upward again 

 to the north, and, reclining upon the granite, forms a shallow synclinal 

 valley. The drift-material deposited by Tomichi Creek is quite consid- 

 erable, and hinders somewhat in recognizing structure ; but the yellow 

 and brownish sandstone capping the granitic bluffs in the western por- 

 tion of Tomichi Valley is probably Lower Cretaceous. In the eastern 

 part, the dip is oft' from the trachorheitic mountains to the westward ; 

 while from the western end, the dip is southeastward. Wherever the 

 characteristic yellow and gray shales occurred, considerable quantities 

 of fossils were observed, but, strange to say, never anything besides 

 Ostrea and Inoceramus. Over westward, toward station 41, the shales 

 have disappeared almost entirely on the northern side of the valley, 

 and nothing but the lower sandstones remain. It seems probable to 

 me that the Cretaceous rocks extend, at least for some distance to 

 the south and southeast, under the covering trachorheites, judging 

 from the general orographic features of the country, that seem to be 

 more those of a sedimentary one than of a volcanic. The Cretaceous 

 that we find along Tomichi must have come in from the northwest 



