414 Annals of the Carnecjie Museum. 



So they differ in some respects from the gneisses in the region of 

 Virginia City and other places to the southward in not showing traces 

 of stratification. 



The Belt Terrane is here divided into the Neihert quartzyte and the 

 Belt formation. Their total thickness is 5,000 feet. 



Only two or three miles southwest of this area and in part con- 

 tiguous to it the Cambrian is represented as being in contact with the 

 Archaean. 



If we now turn to the Cherry Creek formation and the Ruby crystal- 

 line limestone and gneiss we meet the same difficulties. In the typical 

 locality for the Cherry Creek formation we find by referring to the 

 Three Forks Folio, that, south of Ruby Creek, the Cambrian is in con- 

 tact with the Archaean, while to the north of the creek it is in contact 

 with the Cherry Creek beds. I have' not personally noted the contact 

 here. At the foot of Old Baldy Mountain not far distant I have 

 done so, and there is no trace of the limestones of the Cherry Creek 

 beds. A few miles farther to the west, as stated before, the Ruby 

 crystalline limestones are in contact with the gneiss. 



Why do beds thousands of feet thick thin out so suddenly ? On 

 page 2 of the Three Forks Folio the following statement is made : 

 "To the northward beyond the limits of the district, these beds [Belt] 

 attain a thickness of 10, coo or 12,000 feet. In the northern quarter 

 of the area the Belt formation immediately underlies the Flathead 

 quartzyte but to the southward it is absent and does not intervene 

 between the Archaean and the undoubted Cambrian, and the forma- 

 tion -certainly was not laid down on the Archaean except within a 

 comparatively narrow strip of the northern edge of the area shown on 

 the map, and even here the actual contact has not been seen." 



It seems to me that there are other possible alternatives than the 

 theory that Algonkian rocks were not deposited where they are not 

 now found. It seems incredible that 6,000 or 7,000 feet of sandstone 

 slates and arenaceous limestones should be laid down in one locality 

 and nothing be deposited ten miles or less away. Evidently shores 

 of seas must advance or recede unless the agents which tend to build 

 out the shore lines are exactly balanced by the invasion of the waves 

 and tides. But it hardly seems possible that this could be continued 

 for an inconceivably long age so that fine sediments a mile or two in 

 thickness should suddenly decrease to zero. 



The theory that the Cherry Creek beds and the similar ones of the 



