6io JOHN LYON RICH 



from another small monadnock near the base of Aspen, shows well 

 its character and relation to the surface of the gravels. This, 

 like Aspen, is due to the silicification of a Cretaceous sandstone. 

 Near by there are several other smaller masses of silicified sand- 

 stone projecting through the gravels which in this vicinity are 

 comparatively thin, sometimes not more than ten or twelve feet 

 in thickness. 



Character and origin of the gravels. — The conglomeratic capping 

 of the plateau is made up for the most part of gravel and sand of 

 greatly varying texture. In the low area south of Aspen Moun- 

 tain the pebbles are not as a rule more than from one-half to one 

 inch in diameter, and the greater part of the material on the surface 

 is a fine gravel or sandy loam derived from the disintegration of the 

 conglomerate. As one goes south the material gradually becomes 

 coarser till, at the southern end of Miller Mountain, bowlders 

 varying from one to five feet or more in diameter are common. 

 On the south slope of the mountain many large bowlders strew 

 the surface to such an extent that passage with a horse is difficult. 

 From the low area northward to Aspen Mountain the material 

 also becomes coarser. In some of the deep gullies cut into this 

 deposit one may find many bowlders like those shown in the photo- 

 graph, Fig. 6. Diameters of four or five feet are not uncommon 

 in this part of the deposit. The bowlders are subangular for the 

 most part, like those shown in the photograph. They occur 

 imbedded irregularly in finer gravels and sand. 



The gravels are rudely stratified, but in ordinary exposures the 

 stratification cannot be seen well. At first the deposit at the base 

 of Aspen was thought to be of glacial origin on account of the large 

 size of the bowlders, their subangular nature, and their occurrence 

 scattered irregularly through the finer gravels. Later this idea 

 was abandoned on account of the complete absence of striations 

 on any of the bowlders, the lack of any signs of glacial action on 

 the bed-rock underneath, and finally on account of the local nature 

 of any possible supply ground. Aspen Mountain from which the 

 material came is too small to have supported glaciers under any 

 circumstances. 



South of the low area the gravels consist largely of red and 



