W. Upham — Recent Fossils near Boston. 201 



Art. XXIY. — Recent Fossils near Boston ; by "Warren 



Upham. 



[Read before the Boston Society of Natural History, Nov. 4, 1891.] 



Fossil marine shells of the Postglacial or Recent epoch 

 have been lately discovered at several places in the vicinity of 

 Boston, indicating slight postglacial changes in the relative 

 levels of land and sea, and proving considerable changes in the 

 temperature of the sea there. These fossils have been care- 

 fully collected and studied by Miss D. L. Bryant, of the class 

 of 1891, Massachusetts Institute of Technology ; and, with 

 topographic and geologic notes of the localities of their occur- 

 rence, they were the theme of her graduating thesis, to which 

 I am indebted for a large share of both the observed facts and 

 the conclusions drawn from them, as here presented. Another 

 interesting collection has been made by Mr. Collier Cobb, of 

 the Institute of Technology, instructor in geology and palaeon- 

 tology. Miss Bryant gives lists of species obtained by excava- 

 tions and dredging in three localities. 



1. Grading and deep trenches along the valley and estuary 

 of Muddy River, adjoining Brookline and forming the western 

 continuation of a new park of the city of Boston, encountered 

 a fossiliferous clayey stratum a few feet thick, lying near the 

 present level of low tide, underlain by stratified clay, and 

 directly overlain by a bed of peat about one foot thick, which 

 is succeeded by the latest fine muddy alluvium of this stream, 

 from 5 to 12 feet in thickness. In the upper part of the clay, 

 the thirteen species noted by asterisks in the first column of 

 the following table were found, occurring in abundance to- 

 gether, except that the oysters were restricted chiefly to one 

 place. 



2. In the dredging of the Charles River during the con- 

 struction of the new bridge from the Back Bay district of 

 Boston to Cambridgeport, at a distance about one and a half 

 miles west of the State House, there was brought up first river 

 mud, which had a thickness of several feet, and next sand con- 

 taining shells of twelve species noted in the second column of 

 the table. The river here is a broad tidal estuary, a great part 

 of which has been filled and now constitutes the Back Bay 

 district ; and the ground where these fossils were dredged 

 forms part of the deepest channel of this bay or enlargement 

 of the Charles River back of the original peninsula of Boston. 

 The fossiliferous sand was ten feet or more below mean low 



Am. Jour. Sci.— Third Series, Vol. XLIII, No. 255.— March, 1892. 

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