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least, of the agates, which so abound in the altered rocks, adjoin- 

 ing the dykes of trap, from amygdals of chlorite ; and various 

 specinnens were exhibited, showing the stages of transition from 

 the one to the other. 



Prof. R. next referred to the interesting question of the age of 

 the red sandstone and conglomerate of Lake Superior, about 

 which geologists have been much divided in opinion. The 

 absence of any clear sections showing the place of this formation, 

 in relation to the other strata of Michigan, and the non-existence 

 of fossils in it, had hitherto made its date merely conjectural. 

 He had to announce, however, that he succeeded, in September 

 last, in detecting the contact of this conglomeritic mass with rocks 

 of a determinate place in the Appalachian series. The peninsula 

 of Kewenaw offers no such contact ; but, going to the neighbor- 

 hood of Chocolate and Carp Rivers, he there discovered the fol- 

 lowing condition of things : First, a group of rocks, the equiva- 

 lents, undoubtedly, of the Primal sandstone and Primal slate, 

 of Professors W. B. Rogers and PL D. Rogers, denominated, in 

 the nomenclature of the New York Survey, the Potsdam sand- 

 stone, and these rocks, highly inclined, and traversed by parallel 

 east-and-west axes. Secondly, upon the uptilted edges of this 

 earliest palaeozoic formation, rests, in an unconformable position, 

 and with a very gentle northern dip, the conglomerates and 

 shales of the red sandstone series. Specimens of the conglo- 

 merate were displayed, in which the pebbles were all from the 

 older rocks. Mr. Rogers thought this fact of unconformable super- 

 position an almost conclusive proof of a post-palseozoic date ; and 

 he proceeded to argue, from various points of analogy between 

 the red sandstone itself, its trappean dykes, and their mineral 

 associations, with the similar components of the mesozoic or new 

 red sandstone of the Atlantic States, that the formation in question 

 is of equivalent age and origin with this last-named interesting 

 group of rocks. 



Some discussion of these subjects was then had by Dr. 

 C. T. Jackson, Prof. William W. Mather, of Ohio, and 

 Prof. Rogers. Prof. Mather then stated some facts ob- 

 served by him, in relation to the geology of the northern 

 shore of Lake Superior. 



