THE BASE OF THE DENVER. 1(51 



but which contains in addition some augite and some clear plagioclase 



particles witli glass inclusions. The strata arc here vertical, with a strike 

 N. 4° to 5 30' \\ ., and the contact plane of sandstone and clay is wavy 



and irregular. At some l(i feet above the contact the sandstone is finer- 

 grained, softer, and contains abundant glassy plagioclase grains, with horn- 

 blende, augite, biotite, and some rounded quartz particles. Above this 

 horizon the section is incomplete, but sandy beds or fine conglomerates 

 appear at intervals, with a rapidly decreasing dip, and in these the particles 

 are all derived from andesites. It is probable, then, that we have here 

 exposed the actual contact line of the Denver and Arapahoe formations. 



outcrops in Kinner Run. — The small water course called Kinner lJun. which 

 enters Grolden from the southeast, near the base of Table Mountain, has 

 cut down into the lower strata of the Denver formation at several points, 

 though it may not have penetrated to the very base. The banks of the 

 ravine east of the court-house show horizontal, crumbling gravel and sand 

 strata in which minute pebbles of andesite are more abundant than quartz 

 grains. Below these layers are clays. Also near the forks of the run. a 

 little south of town, there is a similar contact between sandy beds con- 

 taining small andesitic pebbles and pure clays below. 



THE STRATA OF SOUTH TATiLE MOUNTAIN. 

 General statement. Fol' ,M distance of 30<> 01' 40< > feet above its base tile 



Denver formation is prevailingly made up of fine-grained, friable sand 

 rocks, of clays, and of intermediate mixtures, which are not sufficiently 

 coherent to form good outcrops except under the most favorable circum- 

 stances. In consequence of this character no complete section can lie 

 given of this part of the series. 



The basaltic sheet of Table Mountain which was poured out upon 

 the floor of the shallow Denver sea has preserved the underlying strata 

 from complete destruction, and it is upon the steep slopes below this lava 

 How that all the best exposures in this part of the series are now to be 

 found. While continuous sections are of very limited extent, a good idea 

 of the character of the entire thickness of the strata represented may be 

 obtained by correlating, as far as possible, the scattered outcrops of Table 



MON XXVII 11 



