260 Prof. Rogers's Address before the 



Hudson to the lower St. Lawrence. It has been examined by Prof. 

 Emmons and Dr. Jackson in Maine, by Capt. Bayfield, Mr. Lyell and 

 Mr. Logan in the valley of the St. Lawrence, by Profs. Hitchcock and 

 Mather and Emmons in the valley of the Hudson and Lake Champlain, 

 by Mr. Vanuxem on the Mohawk, by Mr. Hall in western New York, 

 and by Prof. Mather on the upper lakes ; and the inferences arrived at 

 by some of these gentlemen respecting the physical conditions under 

 which the formation was produced, are not a little remarkable. 



Among the most instructive exhibitions of the deposit are those of 

 Lake Champlain and the St. Lawrence, where in certain places some 

 very interesting fossils are met with. According to Prof Emmons the 

 mass on the borders of Lake Champlain, consists of a stiff blue clay 

 overlaid by yellowish brown clay and this in turn by a yellowish brown 

 sand, and Prof. Mather mentions that in many parts of the Hudson val- 

 ley these are surmounted by gravel. More than twenty species of ma- 

 rine shells have been procured by Prof. Emmons from the blue clay on 

 the St. Lawrence and Lake Champlain, the two most generally diffused 

 being the Saxicava rugosa and Tellina Grcenlandica. The greater 

 part if not all of these species, it is stated by our conchologists, now 

 live either on the coast of Massachusetts, or in the Gulf of St. Lawrence, 

 and they therefore imply a climate at the period of the clay deposit, as 

 cold at least, as that which the same region now possesses. Although in 

 the Hudson valley and throughout still wider limits, the blue clay is des- 

 titute of fossils, its identity with the stratum of Lake Champlain is not 

 doubted by Profs. Mather and Emmons. The formation though gener- 

 ally thin, attains at certain points on Lake Champlain a thickness of 

 one hundred feet, and Prof. Mather states the whole depth at the town 

 of Hudson, to be one hundred and eighty four feet. It is worthy of re- 

 mark that the upper surface of the deposit rises in some places in the 

 Champlain valley, to an elevation of between two hundred and three hun- 

 dred feet above the lake, or more than four hundred feet above the tide, 

 and this agrees with its highest level in the valley of the Pludson,* At 

 Montreal the same stratum has an elevation above the tide of between 

 six hundred and seven hundred feet. These facts have been considered 

 as indicating that a wide tract of the continent, as far south at least as 

 latitude 42°, stood depressed during this recent tertiary epoch below its 

 present level, to the extent of four hundred or five hundred feet, and 



* For the above and other facts, consult Reports on New York survey by Em- 

 mons and Mather. 



