170 GEOLOGY OF THE DENVER BASIN. 



of leaves and stems of plants. A collection was made at tliis place in lss3 

 and the specimens were placed in the hands of Prof. Lester F. Ward for 

 identification. 



EXPOSURES ON NORTH TABLE MOUNTAIN. 



The slopes of North Table Mountain are both higher and steeper than 

 the average slopes of South Table Mountain, but there are no outcrops of 

 Denver strata here that are of special importance. Near the basalt there 

 are frequent exposures of a dark conglomerate bed of very variable thick- 

 ness. On the west side of the southeast gulch an outcrop at the contact 

 with the main basalt sheet shows the contact surface cutting down obliquely 

 from the north across about 10 feet of strata, but whether this is due to a 

 plowing action of the basalt or to earlier causes can not be determined. 

 The horizon of the lower basalt streams is situated quite uniformly at 100 

 feet below the capping sheet, and is at the top of the beds included under 

 3 of the section already given. These basaltic streams, which are described 

 in detail in the chapter on eruptive rocks, must have been poured out upon 

 a sea bottom and quickly covered by sediments, as is plain from their 

 texture and the fact that they are overlain by sandy beds of material simi- 

 lar to those upon which they rest. The best locality for examining the 

 relations of these streams to the Denver strata is on the southern slope of 

 the mountain, midway between the two large gulches. Here the upper and 

 lower contacts of a small basalt stream, as well as those of the upper sheet, 

 may he clearly seen, and also a number of characteristic beds of the Denver 

 series. 



In the sandy strata of a horizon slightly above the basalt streams are 

 found isolated angular specimens of pale bluish-gray augite-andesite, in 

 structures varying from the massive to the very porous forms. The same 

 rock is also occasionally found on South Mountain and on Green Mountain. 

 It is not demonstrable. that all loose pieces come from a single horizon, but 

 it is quite probable that the one above referred to contains nearly all of 

 them. In the cavities of the porous variety are found chalcedony, quartz, 

 and heulandite, and in some fragments the new zeolite species, ptilolite. 



A distinct spherical sundering was noticed in certain sandy beds not 

 far below the basalt on the northwestern slopes of North Table Mountain. 



