CAMBBIAH LAND. [5 



and the Gore mountains, which may then have formed parr of the Park 

 Range, and consequently of the western shore of the Colorado Island. It 

 is probable, though less certain, that a water connection also existed through 

 Canyon Citj Bay with the eastern sea; but it' deposits were formed in this 

 strait they have since been removed by erosion and can no longer be traced 

 continuously. Only Mesozoic or later beds are now found in contaci with 

 the elder crystalline rocks on the west Hanks of the present Colorado 

 mountain range, which conceal the older deposits, so that the position of 

 the ancient shore-line can he only approximately determined. This is also 

 true of a considerable portion of the eastern shore-line. 



EARLY PALEOZOIC SEDIMENTS. 



The deposits formed in the early Cambrian seas around these islands 

 were continued through Silurian into early Carboniferous time in a sort of 

 cycle of deposition: that is. the successive beds formed during these 

 periods show in their present outcrops no decided discrepancy of angle or 

 other evidence of any pronounced orographic movement during the period 

 which would have sensihlv changed the form of the land masses around 

 which they were deposited. That the region as a whole was subjected to 

 changes of level with reference to that of the surrounding water, and that 

 probably there were some local movements of elevation ami subsidence 

 producing differential changes of level on different portions of the shore- 

 line, is evidenced by certain observed unconformities hv erosion, generally 

 ■of small amount, and by the thinning or even complete absence of some of 

 the series of beds at certain parts of the observed outcrops. The thickness 

 of beds deposited during this cycle of deposition was very slight, especially 

 along the eastern shore, where in no case, as far as observed, does it exceed 

 an aggregate of 350 to 4uo feet. They consist mainly of sandstones, more 

 or less calcareous, and of siliceous limestones with some shales, generally 

 in subordinate development. The series increases in thickness to the west- 

 ward, being 500 to Tod feet around the Sawatch uplift, about 2,000 feet in 

 the Grand Canyon region, ami reaching an aggregate of 15,000 to 20,000 

 feet in the longitude of the Wasatch Mountains. 



In these outlying regions there is, as in the Rocky .Mountain region, no 

 evidence of any pronounced orographic disturbance during the deposition 



