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Association of American Geologists and Naturalists. 261 



Profs. Emmons, Mather and Hall, and Mr. Vanuxcm, rest some interest- 

 mg speculative views concerning the physical geography of the region 

 in the period of the drift, upon this conclusion. 



Here I may be permitted to suggest a caution. We are not I believe 

 yet assured that the clay deposit in all districts belongs to one formation, 

 or is the product of a single epoch, and especially we are destitute of 

 proofs that the stratum which occurs on the great lakes, excepting that 

 on lake Ontario, is of oceanic origin. The clay on the Detroit river is 

 fossiliferous, but whether the shells are lacustrine or marine has not, I 

 believe, been ascertained. Should they prove to be identical or nearly 

 so with those of the St. Lawrence, then the whole amount of depression 

 of the land required to let in the ocean to the present basins of the 

 Upper Lakes, as supposed by Prof. Mather, must be conceded ; but for 

 the determination of this identity further observation is required.* 



As it has been shown by Mr. Lyell and others, that several of the 

 fossils found in this deposit at Port Kent on Lake Champlain and at 



eauport on the St. Lawrence, are identical with species found by him 



Wdde valla, and elsewhere in Sweden, and known to frequent the 



colder latitudes at the present day, he and other geologists conceive that 



e y behold in these facts, proofs of an arctic climate, and this inference 

 "^ been made to bear on the hypothesis of the origin of the drift. 



ut Slnc e nearly all of these shells are stated to exist at present in the 



u 'f of St. Lawrence and on the coast of New England, they do not 

 Necessarily imply a decidedly colder temperature in the waters than 

 ^y now prevail in certain parts of the great Labrador current. 



^addition to the proofs afforded by this post pleiocene formation, of the 

 °rmer lower level of the land and of the nature of the climate, it leads to 

 ^me important inferences connected with the epoch of the still more ex- 

 tensive drift formation of the same region. It has, I think, been satis- 

 «ctorily established by Profs. Hitchcock, Mather and Emmons, that the 

 lue fossiliferous clay is newer than that period of erosive action which 

 Messed the scratching and polishing of the rocky floor throughout the 

 n °1hern part of the continent, for not only does the deposit rest on that 

 Rated surface, but there often intervenes, according to Prof. Mather, a 

 a of gravel and bowlders, which he views as a part of the drift itself, 

 ^"gh from this conclusion Prof. Emmons and Mr. Hall seem, if I 



^nce this address was written I have been informed by Prof. Mather that he 

 8 examined the fossils of the clay of the Detroit river and found them to apper- 



ssclusively to fresh-water species. 



01 tt TO| No. 2.-Ju]y-Scpt. 1844. 34 



