84 



BULLETIN OF THE 



of the Porcupine ranges that, " while we desire to avoid any theoretical 

 conclusions as to the mode of their formation, we cannot but observe 

 that the character of the entire trap formation is rather that of a succes- 

 sion of overflows, than of simultajieous uplift in mass ; in other words, 

 it may be considered as made up of hech of the different kinds superim- 

 posed upon each other." He also regards the " epidote veins " as in the 

 main contemporaneous beds whose mineral contents were deposited 



with the bed. 



Dr. D. D. Owen, in his Ecport of a Geological Reconnoissance of the 

 Chippewa Land District of Wisconsin, etc.,* of the date of April 23d, 

 1848, regarded the sandstone of Lake Superior as younger than the Car- 

 boniferous age, basing his conclusions, as Dr. C. T. Jackson had done, 

 on lithological and mineralugical characters only. {l. c, pp. 57, 58.) 

 In his final report (Oct. 30th, 1851, pp. 187-193), this view was aban- 

 doned, and the sandstone regarded as Potsdam. 



Dr. C. T. Jackson t remarked in 1848 that the sandstone agreed in 

 its characters with those of the oldest of the sandstone formations. On 

 Jan. 2d, 1850, (l. c, p. 228,) he stated that he wished to correct the 

 record, as the preceding view of the age of the sandstone should be 

 accredited to his assistants, Messrs. Foster and Hill, and not to himself. 



Mr. James T. Ilodge -t seems to regard the veins as filled by igneous 

 injection and sublimation. The silver was injected after the copper 

 had cooled and occupied the spaces left by the contraction of the latter 



on cooling. 



Dr. Charles T. Jackson in his report (pp. 302, 398, 399, 471-473),§ 

 transmitted November 10th, 1849, stated that the amygdaloid was 

 formed by*' the interfusion of the rod sandstone and trap," and the 

 trap rocks are distinctly stated to have burst through and between the 

 strata of the pre-existing sandstone. He calls attention to the mooted 

 question whether the trap rocks originated from the molten interior of 

 the earth, or were derived from the re-fusion of'the lower stratified rocks 

 (p. 397). The sandstone and conglomerate are said to have been de- 

 rived from granite, gneiss, or mica slate and porphyry. The porphyry 

 is thought to have resulted " from the semifusion of the finer materials 

 of the sandstone. It' is evident at once, from inspection of the pebbles 



* Senate Documents, Ist Sess., 30th Cong., 1847-48, VIL, Doc. 57, 134 pp. 



t Pi-oc. Bost. Soc. Nat. Hist., HI. 76, 77, Nov. l.st, 1848. 



t Proc. Am. Ashoc. Adv. Sei., Aug. 20th, 1849, II. 301-308. 



§ Senate Documents, 1849-50, HI. 371-935. See also Proc. Am. Ass. Adv. Sci., 

 H., 1849, Aug. 20, pp. 233-301 ; Bulk Geol. Soc. France, (2,) V(d. VII., 1849-50, 

 pp. 667-673, and Am. Jour. Sci., (2,) Vol. X., 1850, pp. 65-77. 



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