AMERICAN GEOLOGY DECADE OF 1840—1849. 4 1 ( d 



arrangement of the earthy gangues, all seem to indicate the existence of electrical 

 currents during the period of their formation. 



Concerning the origin of the drift and the phenomena of the groov- 

 ing^ and striationsof the rocks in the regions, they were still somewhat 

 in the dark. The position of bowlders resting on stratified deposits of 

 sand and clay was regarded as antagonistic to the theory of a general 

 ice cap similar to that of the circumpolar region. It was thought 

 that such might rather have been transported by floating ice (not ice- 

 bergs) in the same manner that bowlders are even now each spring 

 transported from the borders of the northern lakes and rivers and 

 dispersed over the adjacent swamps and lowlands. 



The slates of the region were looked upon as probably originally 

 laid down as volcanic ashes and subsequently consolidated — a by no 

 means improbable theory. The specular and magnetic iron ores they, 

 strangely enough, regarded as 



a purely igneous product, in some instances poured out, but in others sublimated, 



from the interior of the earth. We may conceive that the various rocks of the Azoic 

 series were originally deposited in a nearly horizontal position. During the deposi- 

 tion of these strata, at various intervals sheets of plastic matter were poured forth 

 from below and spread out upon the surface of the pre-existing strata. During this 

 period the interior of the earth was the source of constant emanations of iron, which 

 appeared at the surface in the form of a plastic mass in combination with oxygen, 

 or rose in metallic vapors or as a sublimate, perhaps as a chloride: in the one case it 

 covered over the surface like a lava sheet, in the other it was absorbed into the 

 adjacent rocks or diffused through the strata in the process of formation. 



The igneous rocks they classified as dolerite, anamesite, and basalt. 

 The sandstone, which occupies almost exclusively the bed of Lake 

 Superior and which occurs in isolated patches along the shore and on 

 the islands, they rightly classed as Potsdam, differing in this respect 

 with Jackson, who considered it as New Red, and from Locke and 

 others, who thought it to be the equivalent of the Old Red or Devonian 

 sandstone of Europe. 



The work on the Paleozoic rocks, as given in Part II of these 



reports, was done by James Hall, of New York. The limestones 



iirst seen upon St. Marys River, Hall regarded as identical with the 



Chazy, BirdVeve. Black River, and Trenton lime- 

 nails Report on * , * l , t 



Lake Superior stones of .New 1 oi'k. The Cliff' limestone of Owen he 



Rocks. 



designated as the Galena limestone, which he errone- 

 ously regarded as a distinct member of the Lower Silurian system. 

 not recognized in the East. 



In his chapter on the parallelism of the Paleozoic deposits of the 

 United States and Europe, Hall called attention to the fact that — 



The simplest principles of elementary geology teach us that sedimentary beds, 

 having the same thickness and same lit hographical characters, can not have spread 

 over an area so wide as that now included between the European and American 

 continents. All sedimentary deposits must vary in character at remote points, as 



