174 GEOLOGY OF THE DEXVER BASEST. 



thought to be the equivalent of that found just below the basalt of Table 

 Mountain. The reasons for this are the apparent correspondence as to 

 horizon and the great similarity of composition, although it is recognized 

 that the latter fact would prove little in the light of the known variability 

 of the strata of such constitution. If this conglomerate is the equivalent of 

 the Table Mountain bed we have a nearly complete section of the forma- 

 tion by combining the two exposures. 



The stratum on the line of profile has a strike N. 15° 30' W., with 

 an easterly dip of 45°. It occurs along the entire western base of the 

 mountain at or a little below the steeper slopes, and it can be traced 

 continuously in either direction until the low approaches to the mountain 

 are reached. 



At its base this division is composed of dark sand with a few small 

 andesite pebbles. In the central and upper parts it shows pure conglom- 

 erates with sandy layers interstratihed. The latter are seldom continuous 

 in the body of the conglomerate, their form being that of wedge-shaped 

 masses with marked cross-bedding, shown both by their stratification and by 

 their relation to the conglomerate proper. A similar cross-bedding is also 

 apparent in the conglomerate itself, so that determinations of dip and strike 

 can be made only by observing the course of the bed as a whole. The 

 pebbles are mostly small, but few reaching a diameter of 4 to 5 inches, the 

 majority being less than '2 inches. The rocks represented by the pebbles 

 are nearly all dark, and there does not seem to be as much variety here as 

 in Table Mountain. Few of them are porous. They lie in a scanty matrix 

 of sand composed entirely of debris of andesitic rocks, while the actual 

 cementing material is chiefly zeolitic in nature. In the small, irregular 

 spaces between larger pebbles may occasionally be found cavities lined by 

 small crystals of chabazite or stilbite, or in other cases tilled by yellow 

 calcite. Isolated augite crystals are abundant in the sandy matrix, but they 

 are less perfect in form than those of the Table Mountain conglomerate. 

 A few Archean pebbles were found in this conglomerate after careful 

 examination of a considerable area. 



The distinctly conglomeritic portion of Division B is actually 25 feet 

 in thickness. The remainder of the 50 feet assigned to it is chiefly at the 



