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BULLETIN OF THE 



Dr. Douglas Hongliton, in his first Report on the Geology of Miclii- 

 gau, remarks upon the "appearance of primary and, trap rocks forming 

 mountain cliaius, and tlio groat disturbance which has taken place 

 since the deposition of the red sandstone," and says tliat this sandstone 

 in the vicinity of Granite Point is "scarcely disturbed, resting upon 

 nobs of primary rocks." * In Dr. Iloughton's Fourth Annual Report, 

 for 18.11,t tlie rocks of this region are described as primary ones, con- 

 sisting chiefly of granite, sienite, sienitic granites, and greenstone witli 

 metamorphic rocks on their flanks, forming a stratified series consist- 

 ing of "talcose, mica and clay slates, slaty hornblende rock, and quartz 

 rock ; the latter rock constituting by far the largest proportion of 

 the whole group." He considered tliat the granite passed "ahiiost in- 

 sensibly into a serpentine rock." {I. c, p. 482.) In like manner, he 

 thought that the granites on the soutlicastcrly side of the district 

 changed going northwesterly into a greenstone, and tluit the dikes trav- 

 ersing these granites were identical with the greenstone, having been 

 injected into the granite. His serpentine bears a close resemblance to 

 greenstone, and he states that " possibly a more close examination may 

 show it to be a simple series of dUics, lying parallel to the hnc of cleav- 

 age of the slate rocks." {I. c, p. 494.) Regarding Tresque Isle he says : 

 ""rhis point of land has its origin from the simple elevation of a mass of 

 trap rock, which rises on the north in abrupt cliffs, varying from twenty 

 to sixty feet in height. The trap is mostly greenstone, though portions 

 of it are so largely impregnated with a dark-coloi-cd, almost black ser- 

 pentine, as to deserve the name of serpentine rock. The knob of trap 

 under consideration is possessed of additional interest, from the un- 

 equivocal evidence of uplift, as also from the manner in which these 

 evidences are exhibited. The cliffs of trap occupy the very extremity 

 of the point, while the neck and central portions are made up of con- 

 glomerate or trap tuff and sand-rock, resting .nptm the trap. These 

 upricr rocks also appear upon the immediate coast, in cliffs of from 

 twenty to sixty feet in height, and in many places they are seen resting 

 directly upon tlic trap. The stratification of those sedimentary rocks 

 has been very much disturlied, and they invarialily dip, at a high angle, 

 in all directions from the trap itself. The character of liotli rocks, at the 

 immediate line of junction, is almost completely lost, and the evidences 

 of change most unequivocally marked. But the most curious feature 

 of the whole is, that the sedimentary rocks, for a distance of several 



« History of Micliig™, T.y ,T. H. Lunmaii, (New York, 1S39,) pp. 318, 352. 

 t Joint Docuun-nls, Jliefiig;iii, 1811, pp. 471-007. 



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