4* 



MUSEUM OF COMPAKATIVE ZOOLOGY. 



85 



of the conglomerate, that they have been ground into their present 

 shape by long attrition under wiitcr, or upon some ancient shore. 

 .... They originated from some nether rock, or were transported 

 to their present kcation by drift agencies." Dr. Jackson will then 

 stand next iu order of time to Rev. J. G. Gumming in suggesting the 

 idea of drift agencies in the earlier geological periods.* May wo sug- 

 gest that these conglomerates are the lateral moraines of the ancient 

 glaciers which scooped out the basin of Lake Superior, and that the 

 coldness of the waters at the time of the melting of these glaciers pre- 

 vented the existence of hfe then. In this way we account for the Lake 

 basin, the conglomerates, and the absence of fossils, three difficult prob- 

 lems. As we now know the geological structure of the country to be dif- 

 ferent from that supposed by Dr. Jackson, there exists an excellent field 

 here for speculation concerning the number of glacial periods during 

 the time of the deposition of the rocks of Keweenaw Point, the con- 

 nection of glaciers with volcanic action and the eccentricity of the 

 earth's orbit. It is very probable that the ice by its weight carried the 

 sedimentary strata downwards, the same pressure aiding in their igneo- 

 aqucous fusion (solution), while the thickness of the ice mass would 

 cause the gcothermal couches to rise, thus enabling us to account for 

 the lavas. This leads us to the consideration of the ofToct that glaciers 

 may have in forming lake bottoms by their pressure bending the under- 

 lying strata, the displaced material being erupted along the sides of the 

 depression. We can thus account for the proximity of volcanoes to 

 large bodies of water, and explain the cause of the highest mountains 

 being adjacent to the deepest oceans, their successive elevations cor- 

 responding to the different glacial epochs. If the Atlantic is to be 

 filled with a solid mass of ice to account for the loess of the Rhine, and 

 the Southern oceans to be filled in like manner to explain the geographi- 

 cal distribution of the New Zealand faima, why cannot Lake Superior 

 also be filled, wlien it will cost so little and explain so much'? 



Dr. Jackson further considers the sandstone as belonging to the New 

 Red, stating that it has been absolutely proved not to be Potsdam. He 

 seems to have receded from his former views regarding the filling of the 

 fissures by vein material and not to have adopted any others in their 

 places, lie would, however, consider that the copper and silver *' were 

 produced by igneous agency The copper and silver occur on 



* History of the Isle of Man, 1848, p. 89. So^i also F. B. irough, Proc. Am. 

 Assoc. Adv. Sci., 1851, VL 262-264 ; and the Quart. Jour. Geol. Soc, VI. 96, 97, 

 1850, K Godwin Austin ; XI. 185-205, 1855, A. C. Ramsay. 



