EKDLICH.] DEVONIAN. 211 



throughout the entire district, has probably furnished a large portion of 

 the material to which the quartzites of that region owe their existence. 

 Lithologically it is so characteristic that an outcrop at any other place 

 must necessarily have been identified with it ; and it is to be hoped 

 that the explorations during the summer of 1875, during which time 

 the eastern limits of the metamorphic area can be studied more in de- 

 tail, will throw additional light upon its position in the geological scale. 



DEVONIAN, 

 f 



Of by far greater importance than the preceding isolated outcrop is 

 the area covered by Devonian strata. One feature adds greatly to the 

 interest of this group. It is the fact that at some points more exten- 

 sive deposits, in a vertical direction, are found than at others, both, 

 however, resting directly upon the metamorphic rocks. In character, 

 both lithological and paleontological, the beds, although considerable 

 distances apart, agree very w r ell. 



Upon reaching the summit of the pass that leads from Baker's Park 

 into the lower valley of the Animas, a light-blue to grayish limestone 

 is observed, in positu, dipping to the northward. It is very similar to, 

 if not identical with, the limited outcrop at the head of Cunningham 

 Gulch, where it rests upon the shistose rock, and is covered by trachyte. 

 This limestone formation continues along the edge of the mountains, 

 descending into the canon and keeping a course of outcrop approxi- 

 mately parallel to that of the Animas. Section II, given in the discussion 

 of the Carboniferous, will show the position of the limestone with refer- 

 ence to overlying and underlying strata. Weathering in steep bluffs, 

 of no very considerable height, however, this rock presents a striking- 

 appearance all along the regions of Lime Creek down to the junction of 

 the latter with Cascade Creek. Rhynchonella, Spirifer, and numerous 

 remains of Crinoids that are found at almost every point of exposure 

 facilitate the identification. For the entire series of strata at that lo- 

 cality, a thickness of 1,200 to 1,500 feet may be given. This, as will 

 be seen below, is by far more than the thickuess of parallel beds at any 

 other point. But little variation in the lithological and strati graphical 

 conditions takes place. Above the limestones the Carboniferous beds 

 begin, while they are underlaid, probably for a considerable distance, 

 by the Silurian sandstone. This was observed, however, only at one 

 point. It seems that the metamorphosing agent, that thoroughly 

 changed a large portion of the Devonian strata farther south, either 

 did not reach to the region that has just been discussed, or that an 

 abundance of material underlying the Devonian rocks was sufficient 

 to exhaust its force. 



A. second outcrop belonging to this formation occurs immediately on 

 the southern boundary of the metamorphic area, running in a north- 

 westerly direction from station 48. This station is located on an iso- 

 lated patch of Devonian limestone, surrounded on all sides by metamor- 

 phic granite. Besting immediately upon this granite, which showed a 

 very marked stratification, conformable with that of the superincum-. 

 bent sedimentary beds, a white to red and brown quartzite was found. 

 At some points the contact of the latter with the granite was so inti- 

 mate that specimens could be obtained, showing both the granular 

 quartzite and the coarse-grained granite on the same piece. No definite 

 relation of tue colors exhibited by the quartzite could be established, 

 save the general rule that the nearer it was to the underlying meta- 

 morphic rock, the more intensely it was colored. Proceeding in a south- 



