350 GEOLOGY OF THE DENVER BASIN. 



drifts extending into it from 10 to 50 yards. From some of these 

 considerable coal 1ms been taken, notably one a few hundred yards east 

 of the Marshal] No. 5 mine. It is also stated that the coal at a distance of 

 50 yards from the entrance of this opening abutted against a heavy sand- 

 stone, an occurrence which, with the topographical drop in the ground 

 above and the position and succession of the strata in connection therewith, 

 is strong evidence for the existence of the Bluff fault. 



The Marshall no. 2. — This mine lies beneath the western slo] f the 



Davidson mesa, in the partially depressed interfault block between the 

 southern and middle branches of the Marshall fault system. It is opened 

 by a drift from the gulch to the south, the seam dipping 10° to 15° S\V. 

 The area of coal workable from the mine is limited on the east by the 

 natural thinning of the bed, by the crumpling at the crown of the arch 

 on the western rim of the general syncline, and by the fracturing which 

 was a concomitant feature of the folding. Aside from the numerous throws, 

 which are all small, the coal seam, alter passing the arch and assuming the 

 high easterly dip of the syncline, crosses in outcrop to the southern side of 

 the Marshall Gulch, there ascends the bluff in a westerly direction and 

 unites with the coal of the upper bench, which has already been followed 

 east to this point. In its western extension, within the interfault block 

 itself, the coal of the No. 2 mine passes in its dip beyond the union of the 

 middle and main branches of the system and becomes continuous with 

 the coal opened in Marshall mines Nos. 1 and .'5 and in the Fox mine. The 

 link between the upper and lower benches of the Marshall tield is thus 

 completely established. 



The coal of this mine is hard, bright, and solid, notwithstanding the 

 fact that it has a cover of only 15 to 25 feet of sandstone (C) and shales. 

 Its thickness in the central and western part of the mine is from 8 to !) 

 feet: at the eastern end, 1 feet. The mine has been extensively worked, 

 but is now reduced to a minimum of production — perhaps abandoned 

 altogether. 



THE ALLEN-BOND DISTRICT. 



The Allen-Bond mine. (Fig. M, PI, XX.) This is located 1)11 tile Western 



rim of the Davidson syncline, about 1 mile north of the Davidson mesa. 



