MUSEUM OF COMPARATIVE ZOOLOGY. 9 



occur in vast, irregular masses, like granite ; in clome-shaj»ed, or crater- 

 like summits, as basalt, or trachyte ; in long lines, as dykes or elvans 

 cutting through the incumbent strata; in ramifying veins, like granite; 

 or broad lava sheets, like trap. ]\Iany eminent geologists maintain that 

 the lowest stratified rocks are but portions of the Silurian System, and 

 that, from long-continued exposure to heat, the lines of stratification 

 have become obscure, and all traces of organic remains obliterated. Our 

 observations in this district (they remarked) have led us to a diflferent 

 conclusion." 



" The evidence is ample that the base of the Silurian System reposes 

 upon their upturned edges, and that the causes by which the metamor- 

 phism of the former was effected had ceased to operate before the depo- 

 sition of the latter. Between the two systems there is a clear and well- 

 defined line of demarkation. It forms one of those great epochs in the 

 history of the earth, where the geologist can pause, and satisfy himself 

 of the correctness of his conclusions. On the one hand he sees evidence 

 of intense and long-continued igneous agency, and, on the other, of com- 

 parative tranquillity and repose The Azoic Series was characterized 



bj' immense deposits of specular and magnetic oxide of iron. This might, 



with great propriety, be denominated the Irox Age of Geology 



It was evident that these strata were eveiywhere plicated and folded, 

 and that the observer passed over a repetition of beds, instead of a suc- 

 cession of beds ; but that the strata, throughout the whole region, had 

 been so shattered by earthquakes, and so metamorphosed, by direct or 

 transmitted heat, that it was impossible to identify them, except over 

 limited areas." Later, attention was called to the point that this con- 

 tinent was as old as the European, if not older.* The above points 

 were given in much greater detail in Messrs. Foster and Whitney's 

 " Report on the Geology of the Lake Superior Land District. Part II. 

 The Iron Region, together with the General Geology." Transmitted 

 November 12, 1851.t Such portions of this report as it is necessary to 

 note will be touched upon below. 



The range of quartzose hills extending from Carp River by Teal Lake 

 was described to some extent, and was regarded as formed from a 

 metamorphosed sandstone. Enclosed fragments of jasper and slate, 

 lines of bedding, and obscure traces of ripple-marks were said to have 

 been seen in this quartzite {!. c, pp. 15, 16). Of Presque Isle they 

 said : "The outline of this mass is very irregular, and resembles an im- 



* Same Proceedings, page 151. See also entire article, pp. 136-151. 

 t Senate Documents, Spec. Sess. 32d Cong., III., 1851. 



