: : ie 
and their Geographical Distribution. 493 
ters lay; with ice, thus cutting off from them the 
power of respiration. This is especially evident at 
Wellfleet, the town whence the Boston market is 
now chiefly supplied with oysters, but all of which 
are first transported and planted there from more 
southern waters. i 
Another curious fact which may be interesting to 
the geologist, has been observed at Lowell. In dig- 
ging away a sand-bank, not far above the junction of 
the Concord and Merrimack rivers, which has not been 
known to undergo any alteration within the memory 
of man, there were found, at some 30 feet below the 
surface, some vegetable and animal remains. "They 
consisted of the branches, leaves, cones, and acorns 
of pines and oaks, in a state of perfect preservation, 
and of Unios, apparently perfect: But on examina- 
tion, the earthy matter was found to have entirely dis- 
appeared, nothing remaining but the epidermis, which 
was so entire in its minutest details, that the species 
were as readily made out, as if just from the water. 
I will mention only one other fact, whieh may 
serve to illustrate, how accident, design, or some con- 
vulsion of nature may present us fossils in the imme- 
diate vicinity of living animals of the same species. 
The Western Avenue, or Mill Dam, was built from 
Boston across a broad basin to the westward of the 
city, by which the water is excluded from the region 
between Boston and Roxbury. It is now more than 
twenty years since this was done, and much of the 
land has already been built upon. Throughout this 
whole region, there is a stratum of shells, such as in- 
habit the river on the other side of the Mill Dam, 
3 
VOL. III. — NO. Iv. 
