186 BULLETIN 109. UNITED STATES NATIONAL MUSEUM. 



The "Blue limestone" is probably not the equivalent of the "Bliift 

 limestone" of Lake Michigan, as it seems to belong in the lower po 

 sition to which Mr. Douglass here assigns it. 



The report of assistant geologist Bela Hubbard is dated Janu- 

 ary 24, 1841, and occupies 34 pages. It proposes "to exhibit a com- 

 preh.ensive view of all tlie rock formation throughout the organized 

 counties of the State." It is prefaced by a general section, which is 

 hero reproduced : 



A. Errntic block group, or Diluviums, a, Alluviums, ancient and recent. 



B. Tertinry clays, 



C. Coal measures — Upper coal and shales, lower coal and shales, included sand 

 stones, limestone stratum. 



D. Subcarboniferous sandstones. 



E. Clay and kidney-ironstone formation. 



F. Sandstone of Point aux barques, 



G. Arjcillaceous shales and flags of Lake Huron. 

 H. Soft, light-colored sandstones. 



I. Black aluminous slate. 

 K. Limerocks of Lake Erie. 



Speaking of the " Erratic block group," he says, " this whole de- 

 posit is one of transport by water." And again : 



Whatever may have been the causes which swept these materials over the 

 face of the rocks, whether oceanic currents or bodies of floating ice. the charac- 

 ter of the diluviums, as well as numerous accompanying facts, plainly implleu 

 that they came in a direction northerly from their present beds, and often from 

 great distances. 



Mr. Hubbard devotes six pages to a very intelligent discussion of 

 the physical features of this formation. But it must be understood 

 that the formation which he has in mind is what we often style the 

 "modified drift," 



By "ancient alluvions" he designates v,diat are often termed "la- 

 custrine deposits, embraced between the ancient lake ridge and the 

 present shores of the lakes." He does not here affirm that these are 

 underlaid by the " diluvium," for this, he says, " overspreads the whole 

 interior of the State beyond this separating ridge." Still there is 

 room to suppose that Mr. Hubbard refers only to what appears on 

 the actual surface. By " ancient alluvions " he designates deposits 

 still in progress, like marl, bog iron, and peat. In the ancient 

 alluvion have been discovered bones of the mastodon in Macomb 

 County, and on the Paw Paw River in Berrien County. A vertebra, 

 pronounced by Doctor Sager to be the caudal vertebra of a whale, 

 was found some years previously on the St. Joseph River. It had 

 a vertical diameter of 18 inches, a transverse of 2 feet, with diameter 

 of body, 11 inches; length of body, 10} inches; length of spinous proc- 

 ess, 9 inches; and weiglit of 21 pounds. 



