AMERICAN GEOLOGY DECADE OE 1840-1849. 



415 



recognized the possibility of fissure eruptions us distinctive from the 

 crater eruptions of modern volcanoes. 



The red sandstones of Lake Superior were erroneously regarded as 

 belonging to the New Red series, the opinion being based upon a tract 

 of limestone carrying the fossil Pentamerus oblongus, which was found 

 in the midst of the sandstone near Anse. 



Jackson, it is well to note, was opposed to the principle of the reser- 

 vation of mineral lands by the General Government. He wrote: 



It may be useful to the public to cause geological and mineralogical surveys to be 

 made for their information, but 1 am satisfied that the reservation of mineral lands 

 is a great evil to the country, and that the Government never can derive revenue 

 from such sources, while the restriction most seriously embarrasses the settlement of 

 newly acquired territory. The above remarks are applicable to the whole copper 

 region, and 1 would not advise the reservation of any part of it as mineral land. 



Jackson's chief assist- 

 ants were J. D. Whitney 

 and J. W. Foster, already 

 noted, Dr. John Locke, 

 and Dr. Wolcott Gibbs. 



In 1848, while occupy- 

 ing the chair of zoology 

 and geology at Harvard 

 University, Louis Agas- 

 siz, in company with 

 Jules Marcdu and a party 

 of students, undertook an 

 exploration of the Lake 

 Superior region, the re- 

 sults of which were pub- 

 lished in L850, under the 

 c a p t i o n 



Agassiz's Physical , 



Characters of Lake of Lake 

 Superior, 1848. 



Superior; 



Fig. 48. — Map showing area surveyed by Jackson, and Foster 

 and Whitney, 1847-49. 



its Physical Character, 

 Vegetation and Animals, 

 compared with those of 

 other and similar regions. Marcou would have us believe that this 

 volume marked an epoch in natural history publications in America, 

 this mainly on account of the superior style of its illustrations. Cer- 

 tainly there was much to justify the claim. 



The country was nearly everywhere roadless, and transportation by 

 water possible only through the aid of birch-bark canoes. As might 

 be expected, the purely geological observations were of little value, 

 excepting so far as they related to glaciation. Agassiz argued that 

 the form of the lake was due to "a series of injections of trap dikes 



