endlich.] METAMORPHICS. 191 



decide the question beyond a doubt. Station 48 is located on an isolated 

 patch of Upper Devonian limestone, surrounded on all sides by granite, 

 answering in mineralogical description to the first one above given (a). 

 The Devonian strata are deposited on the granitic strata conformably, 

 both dipping south 15° west, with a dip of from 4° to 6°. Traveling south- 

 ward from station 48 toward station 49, we pass for nearly a mile through 

 a lower sag, the bottom of which is formed by granite. Eising slightly 

 on this granite, a steep bluff is soon reached, composed below of hard 

 quartzites, with sandstones and limestones higher up. All the strata 

 dip conformably with the well-defined strata of the granite, in the direc- 

 tion and at the angle indicated above. From the quartzite into granite 

 the transition is very perfect, although even small specimens can be 

 found showing on the one side granite, on the other a granular red 

 quartzite. Near the top of the bluff the latter is white or yellowish, 

 becoming red and brown lower down. Finally some mica is observed 

 in it, and the feldspar appears as such, until the coarse-grained 

 granite is reached. The metamorphosis is very thorough, and can 

 be admirably studied at this point. So far as I could decide, the 

 granite was formed out of a partly argillaceous sandstone, contain- 

 ing some iron in an oxidized state, while the purer sandstones were 

 turned into quartzites. Probably the process of metamorphosis was 

 a very slow one, and lasted a long time. Throughout the stratifi- 

 cation is well preserved in all the rocks of that group, but partic- 

 ularly so in the granite of the locality just described. Even the thick- 

 nesses of the various strata which have been altered into granite, cor- 

 respond approximately to those at present exhibited by the superincum- 

 bent beds. At that point, i. e., a short distance north of station 48, the 

 granite overlies the dark schists, which in turn seem to be younger 

 than the true quartzites forming the main bulk of the mountains still 

 farther north. Another locality was observed, where the metamor- 

 phics showed their intimate connection with unchanged sedimentary 

 beds, although not so clearly defined as at station 48. West and southwest 

 of station 38, on the west side of Animas Canon, there appears in the ravine 

 below the station a coarse-grained, white sandstone, that, from strati- 

 graphical reasons, I refer to the Upper Silurian. By following out the 

 course of this sandstone, it will be found that it gradually changes into 

 a white and gray, very compact quartzite. To establish the precise local- 

 ity where this change occurs, did not succeed. 



Besides this direct evidence, pointing to the origin of the metamor- 

 phics under consideration, their geoguostic features are similar, in 

 fact at many places identical, with those that sedimentaries would have 

 exhibited under the same circumstances. Not at any point along the 

 border of this group did we find rocks that were older than Devonian, 

 with the exception of that white sandstone near station 38. Taking 

 into consideration, therefore, the observed conformity of the underlying 

 metamorphics with the overlying sedimentaries ; taking into considera- 

 tion, furthermore, the analogous character of stratigraphical relations, 

 the conclusion must be reached that those sedimentary beds, which 

 existed below the Devonian, furnished the material for the metamorpbic 

 masses. The presence of the sandstone near station 38, which was not 

 observed at any other point, speaks for the existence at one time of 

 sedimentary beds below and conformable with those we now find. 

 Almost, if not entirely, the Silurian has disappeared, and at some local- 

 ities only the highest strata of the Upper Devonian remain, while at 

 others many hundred feet are yet unaltered. Altogether the region is 

 of the highest interest, and it can only be regretted that very uufavor- 



