188 GEOLOGY OF THE DENVER BASIN. 



steep dip, beyond which there is a gap of nearly a mile. The strike and 

 dip must be continued unchanged in this covered area, however, as the 

 point at 'which the beds reappear, at the northern base of Green Mountain, 

 is in the projection of the last known strikes to the north. 



The form of Green Mountain is characterized throughout by smooth 

 slopes, but there is a certain horizon traceable around its entire mass at 

 which the steep upper slopes give way to more gentle ones. At this general 

 horizon the deep excavations in the mass of the mountain give way to com- 

 paratively shallow ravines in the lower slopes. On the western slope the 

 line between Denver and Arapahoe strata can be approximately determined 

 from the persistent outcrops of the conglomerate of the latter formation, 

 which can be found in vertical position, crossing the ridges between the 

 ravines and minor drains. East of these outcrops there is usually a space 

 iu which at a few points only are found small clay outcrops. All ridges 

 are covered byddbrisof bowlders from the mountain above, and the drains 

 are mostly shallow and grassed over along this line. As all strata of the 

 Arapahoe and the lower ones of the Denver series are vertical or dip very 

 steeply all alone- the western base of the mountain, it is evident that the 

 base of the latter formation must come at a distance above the Arapahoe 

 conglomerate equal to the estimated thickness of the intervening clays 

 In one of the ravines running west in the north part of the mountain 

 distinct outcrops of Denver sandstones were found about 100 yards from 

 the Arapahoe conglomerate in a direction normal to the strike of the latter. 

 At this same outcrop the clays underneath the sandstone seem to be of the 

 Arapahoe. Above this horizon are several outcrops of undoubted Denver 

 strata, and at the base of the steeper slopes there appears the conglomerate 

 bed made up of dark andesite pebbles, which can be followed along the 

 whole western slope of tlie mountain, bearing always the same relation to 

 the Arapahoe conglomerate. These two horizons run nearly parallel at a 

 distance slightly greater than the thickness of the intervening strata, with 

 occasional outcrops between them, and continue to maintain this position 

 until the erosion of the southern slopes of the mountain cuts sufficiently 

 down into the Denver beds to cause the outcrops of their less steeply 

 dipping members to diverge somewhat from the line -of the lower 



