ENBLiCH.] CONCLUSION PROZOIC METAMORPHICS. 103 



readily recognized. Were it possible that the geologist could enter the 

 field with completed maps in his hand, his work might be more thor- 

 oughly done, his time could be devoted more satisfactorily to points re- 

 quiring special investigation, and his results presented would necessa- 

 rily have a greater value. Wherever topographer and geologist can 

 work in perfect unison, however, this feature of comparative incomplete- 

 ness can, in a great measure, be obviated. 



At this place, at the close of my lield-work in Colorado, it may be 

 justifiable to present a brief synopsis of the observations made and de- 

 ductions drawn therefrom. Much will be but a repetition of what has 

 been stated in the "conclusions" of preceding years. By presenting, 

 however, the sum of the results in a concise manner, a more con- 

 nected view of the entire subject may be obtained. It is evident that, 

 in spite of the large area covered, many omissions of characteristic 

 features of each formation will occur. In such cases references will be 

 made to the work of others where the wanting members are supplied. 



A formidable array af formations presents itself for discussion. Some 

 of them are entirely unique in their character, others offer much diflti^ 

 culty as to ultimate position in classification. Slowly are we gaining 

 definite, applicable knowledge of our Western groups. Instead of being 

 studied as such, their relations to over- and under-lying formations are 

 now a matter of serious consideration. Viewed thus, from a more 

 objective stand-point, there is every promise of a comparatively speedy 

 settlement of questions that have heretofore agitated geologists and 

 others. In the subsequent pages a chronological succession of the for- 

 mations will be observetl. An exception is made in the case of the 

 metalliferous deposits, which certainly have not all been formed at the 

 same geological period. 



PROZOIC. 



In preference to the word "azoic," I use the term " prozoic." It pre- 

 sents a more ready definition than the former of the idea that it is in- 

 tended to convey. Many groups of geological epochs are "azoic," but 

 by no means was their genesis, as such, prior to the appearance of life 

 upon the earth. 



Belonging to this group we have, in Southern Colorado, quite an ex- 

 tensive series. It comprises gneisses, granites, various schists, and 

 diorites. Of these the first-named appear to be the oldest. Their 

 position as such may be inferred from their relations to the granites, 

 more particularly. Associated with them are micaceous, chloritic. and 

 hornblendic schists; all of these, howeveu, in subordinate quantities, 

 owing their existence, essentially, to the seemingly accidental predomi- 

 nance of the one or other constituent mineral. It often becomes a 

 matter of considerable difficulty to discriminate between prozoic and 

 metamorphic rocks. But few points can be used in evidence for one or 

 the other view, owing to peculiar relative associations. Petrographic 

 characters avail very little, excepting in case we find diorites. By far 

 more varied and of enormous development are the members of the suc- 

 ceeding group. 



METAMORPHICS. 



Large areas of the districts surveyed are covered by rocks of this 

 group. They represent an almost endless variety. In the reports of each 

 year they have been discussed and their Special features have been noted. 

 It is a difficult matter to draw the line of distinction between the pre- 

 ceding and this group. Although, as a role, the physical characteristics^ 



