184 (iKOLOUY OF THE DE2JVEE BASIN. 



and soon predominate. Such a change takes place within a distance of 

 50 feet, there being continuous stratification from one end to the other 

 of the variable beds. 



The Denver strata in this place are therefore capable of being locally 

 developed as nearly pure sandstones of Axchean debris, and this possi- 

 bility indicates most plausibly that a local source lor such material is iii sar 

 at hand. The loose sandstones and grits of the Arapahoe are distant but a 

 lew hundred yards from this spot, where they seem to have constituted the 

 shore, although actual exposures of the shore-line could not he found. 



Such local variations of the Denver sandstones were found in less 

 marked degree throughout the southern part of the area represented as 

 Denver, from the Platte to Coal ('reek, and it seems probable from this 

 fad that the early Denver sea was quite circumscribed in this direction, 

 where the boundary of present exposures is set liv the overlapping of the 

 Monument ( 'reek. 



OCCUKKENCE OF THE FORMATION. 



As the strata of the 1 >enver formation are, almost without exception, soft 



ami friable and thus easily disintegrated, and as they have been especially 



exposed to erosive agencies, their identification as a distinct formation would 

 have been verj difficult were it not for the protected outcrops of Table 

 .Mountain and the section shown in the mass of Green Mountain. Without 

 these it would have been almost impossible to correlate the scattered out- 

 crops in obscure ravines and drains upon the plains, and main' exposures 

 of clay or fine-grained sandstones would have long gone unrecognized. 



Now that the relations are clear it is seen that characteristic outcrops are 

 really quite common over the greater part of the field. 



It is the aim of this section to describe the localities and special 

 features of the principal exposures known, that it may he easy for others 

 to test the conclusions reached in regard to this interesting series of rocks, 

 the identification of which bears upon several questions of Rocky Mountain 

 geology ami raises, mi the other hand, so many new problems lor future 

 solution. 



Tabic Mountain. — The lower portion of the Denver strata is much better 

 exposed on Table Mountain, near Golden, than at any other place. Here, 



