236 C. R. V\\ HISE — PRE-CAMBRIAN OF THE BLACK HILLS 



Bions often have. This facl is mentioned by Dr. Winchell in describing his 

 mgloraerates in gneissic terran In Professor Irving's and Mr. 



Merriam's Btudiea of northeastern Minnesota, they found in Beveral local il 

 peculiar conglomerate-like rock- in the ancient gneisses and granites. Upon 

 a close i samination, the bowlder-like forma were found to be mingled with 

 others having the most extraordinarily irregular forms, even grading into 

 elongated dike-like areas. They came t<> the conclusion thai these peculiar 



currences were not water-deposited conglomerates. Extremely irregular 

 fragments are found associated with the well rounded ones in the gneiss and 

 granite of the < lolorado range in the neighborhood of i fray's peak. In pla< 

 the fragments throw out stringers and increase in size until they assume 

 irregular dike-like forms or become apparenl layers interlaminated with the 

 coarse granitoid gneiss, jusl as in Minnesota. An examination of many 

 thin sections from the fragment-like areas of these ruck- shows that they arc 

 always completely crystalline in character. In mineral composition they 

 arc often like the crystalline schists which arc cut by the granites. 

 Frequently they differ but little from the granite in which they are con- 

 tained, with the exception thai some one mineral, generally the bisilicate, 

 is much inure abundanl in the fragment-like areas than in the ordinary 

 rock 



It would seem that one who maintains that rucks containing well-rounded 

 bowlder-like forms, which sometimes are found intimately mingled with 

 those of extremely irregular Bhape, occurring in a completely crystalline 

 granular matrix arc water-deposited Bediments, is bound to explain lmw a 

 part of them have so perfectly retained their original forma while the others 

 have become bo curiously distorted. We have seen how profoundly and yel 

 uniformly the forces of metamorphism have acted in the Black Hills frag- 

 mental-; the bowlders are deformed in a common direction. This is well 



known to be true of the semi-crystalline i glomerates of the Appalachian 



n, already mentioned p. 221 . as described by the elder Hitchcock.;] It 



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re I li.ivc ri I red Dr \. < I i Imirable report upon tbe Rainy 



inual Report of lh( - irveyof i u 1887 Pari F). The 



in iiu- memoir Dr. Lawaon describee In great ■ i «- 1 *». i I 



ttea iii>- ai ••■■! pseudo-conglomeratic rock a like 



f which has jusl i n discussed. Hi- conclusion mewhal In the line of 



baa i ii fused and the liquid 



intruded the unfused stlmee t"i r. considerable distance, 



on the fused and unfused aedimente occur tl" ir rocks. Ii 



ii how id.' in-. -i i rocks originated, If th oglomeratii 



ed and unfused materials and ""t by the metamor- 



krd Hitch k, 18GI Hitchcock natiirnii-. ed with tl truo 



niiv different oharaoter, found Ht 

 i , , Vei mi. I'll' 1 in ktricea of tl 



ii phyi \ In thoffl imii 'ii 



and hoi nblende schist. 

 -, are pi obably of Pali ' olosely re- 



contained fragmen italllne character. 



■ . ■ 



-h which thej ii iv< pp. W II, 



eted by Hall 



