188 



AGE OF THE RED SANDSTONES 



If, in the absence of conclusive palseontological evidence, the test of lithological 

 character alone be applied, it must be admitted to favour the view, that they are of 

 the same age as the red sandstones of Virginia, Maryland, New Jersey, Connecticut, 

 and Nova Scotia. Specimens of the red sandstones of the south shore of Lake 

 Superior (in Wisconsin), including the buff beds associated with them, cannot be 

 distinguished from specimens in my collection, procured from the quarries of Seneca 

 Creek, in Maryland, of Acquia Creek, in Virginia, and of Little Falls, in New 

 Jersey ; all of which are generally admitted to be of cotemporaneous origin.* 



Some of the results from chemical analysis seem also to favour the same hypo- 

 thesis. Taken as a whole (though with exceptions^), the sandstones of Lake Supe- 

 rior contain a considerable percentage of alumina, ranging, sometimes, as high as 

 twenty per cent. ; while of silica there is often less than fifty per cent. Their 

 peculiar red colour is due to the presence of a large proportion of peroxide of iron, 



this latter opinion. In the report of the proceedings of the Association of American Geologists for that 

 year, we find the following : 



" Dr. Houghton said, that the sandstone of Lake Superior, lying east from Keweenaw Bay, dips, at a 

 moderate angle, to the south, or a little east of south, and passes under a lime-rock, which he considers 

 to be the equivalent of the Trenton lime-rock of New York; while those conglomerates and sand-rocks 

 lying westerly from Keweenaw Point, and flanking the trap on the north, dip to the north, mostly at a 

 high angle. These last-mentioned rocks arc probably cotemporaneous with the New Red, and were doubt- 

 less deposits during the long interval that marked the upheaval of the trap," &c. 



I have sought for, but not met with, any subsequent statement of Dr. Houghton, reversing this opinion. 



My own first impressions, during the explorations of 1847, favoured the same view of the case. In my 

 provisional Report, of 1848, while asserting that "it is impossible, at present, to decide between these 

 conflicting opinions," I added: "Judging from lithological and mineralogical character, there certainly 

 is strong presumptive evidence, that they were deposited subsequent to the carboniferous era." 



It is only after a careful review of all the facts bearing on this question, collected by myself and other 

 members of the corps, that I have finally reached the conclusions given in this chapter. I doubt not, 

 that, had Dr. Houghton's valuable life been prolonged, he also, after examining the problem in all its 

 bearings, would have seen cause to give the weight of his authority to the opinion, that the red sandstones 

 in question are of Lower Silurian date. 



* It was formerly the admitted doctrine, that these sandstones are of New Red date, the equivalent of 

 the Gres de Vosges of Alsace, the Bunt er Sandstein of Germany, and the Triasic System of recent writers. 

 However, the opinion has been advanced by some, that the lower beds of red sandstone running through 

 the older States, are of a date anterior to the coal j perhaps, Upper Silurian ; perhaps, like the sandstone 

 of Lake Superior, which, in aspect and composition they so much resemble, Lower Silurian. With so 

 much uncertainty still hanging over the date of a formation so long submitted to the oldest and most 

 experienced geologists of the Union, it is little surprising that a series of rocks in the remote West, similar 

 to the others, alike in their appearance, and in the absence of acknowledged characteristics, should have 

 caused doubt and variance of opinion, before, at last, after thorough and minute exploration, their true 

 age was satisfactorily explained. 



f As shown, for example, in the following analysis of red sandstone from Madeline Island, one of the 

 Apostle Group, off the south shore of Lake Superior : 



Insoluble silicates, 

 Iron and alumina, 

 Carbonate of lime, 



93-5 

 3-9 

 1-0 



Carbonate of magnesia, 

 Loss, . 



a trace. 

 1-6 



100-00 



