• DENVER OF THE PLAINS. 179 



or sands here and then-, whose characters, as members of the formation, 

 would not be at all clear wen- it not for the continuous section which has 

 been described. 



THE STKA'IA OF Till; PLAINS. 

 The horizons represented. Tile lied of tile Platte at l)ell\< T i> Vertically 



500 feel below the horizontal strata thought to be at or near the base of 

 the formation in dinner Run at Golden, and <;<»<t to son feel below the 

 more or less uneven horizon at which the Denver beds disappear under 

 the .Monument ('reek to the south ami southeast. From Table Mountain 

 toward Denver then- must, then, be a slight dip, enough at leas! to carry 

 the bottom of the formation under the city, ami from the known limit 

 of the strata along the northern line, and from tin- data of the artesian wells, 

 it seems that the base of the series is, in fact, hut little below the river 

 level 'I'his slighi dip is not recognizable in outcrops, for the frequent local 

 variations in planes of sedimentation are greater than the 'lip in question. 



For the same reason one can not determine accurately the thickness of 

 strata actually exposed between Denver ami the southeastern limit of the 

 formation, lint here, too, it seems most likely that it is much less than 

 the vertical interval above mentioned, owing to a slight northerly dip 



All the strata of the plains are considered to he equivalents of the 

 lower 100 feel of the series represented iii Table .Mountain. 



General characteristics. — Although the strata of (ireell and Tallle mountains 



have been described as very fine-grained in the horizons corresponding 



to these deposits of the plains, the hitter are as a ride still liner. This is 

 shown chiefly in the small size of the andesitic pebbles found in the grit 

 or conglomerate layers. Near the western line it is common to find some 

 few larger pebbles, 2 inches or more in diameter, in almost any hed 

 containing pebbles, bul beyond the Platte such pebbles an- very rare. 

 Coarse-grained beds may he searched in vain lor any worn fragmenl a, 

 quarterof an inch in diameter, while smaller ones ma\ lie abundant. This 



fact is of COUrse a natural sequence of the conclusion adopted that the 

 source of the eruptive material was entirely on the western shore. 



A feature of the strata found on the plains is the abundance of nodules 

 in certain sandy layers. These are often :; feet or more in diameter, 



