Tsobases of Postglacial Hlevation.—De Geer. 247 
boniferous, particularly on the southern border. These pebbles 
earry Lingule worm burrows, and more rarely pteropod casts. 
They have been found at Dighton,* Mass., in the Newport con- 
glomerate by Dale;t I have found Lingule in a quartzite pebble 
in the red Carboniferous rocks of Attleboro, and they occur in the 
glacial drift on Gay Head, Martha’s Vineyard, and Nantucket in 
great abundance. These quartzite pebbles, however, do not occur 
in the Neocene gravels, their absence being apparently due to the 
relative ease with which their friable material has been reduced 
to sand in the repeated migrations of detritus which have deter- 
mined the nature of the Neocene gravels. 
The finding of these chert pebbles adds nothing to the evidence 
concerning the probable extent of Cambrian deposits in this part 
of the state at some time in the past, unless it be to indicate that 
we have to look for an extension of the Calcareous series which 
outcrops near Cape Ann,{ at Nahant, and on Mill River, in Wey- 
mouth.@ The general trend of this formation in the direction in 
which we should expect to find the source of the chert pebbles is 
an incentive to more careful search, which it is the object of this 
paper to foster by calling attention to these less easily seen traces 
of the Cambrian sediments and fauna. 
I am indebted to professor Shaler for kind permission to publish 
the notes concerning this collection of fossiliferous pebbles. 
ISOBASES OF POST-GLACIAL ELEVATION. 
By Baron GERARD DE GEER, Stockholm, Sweden. 
After the session of the International Congress of Geologists, 
last summer, in Washington, I made a journey of two months 
along the coasts of New England and Canada and inland along 
the St. Lawrence and Ottawa valleys, with the principal purpose 
of determining the limit of the Champlain submergence and the 
amount of the subsequent post-glacial elevation. The following 
is a brief outline of the results obtained: 
Traces of sea action and marine deposits of Pleistocene age 
*W.B. Rogers: Proc. Boston Soc. Nat. Hist., 1860, Vol. VII, pp. 
389-91; W. W. Dodge, ibid, Vol XVII, p. 406. 
+T. N. Dale: Proc. Newport Nat. Hist. Soc , 1884-5, Doc. 3, p. 9. 
{John H. Sears: Bulletin, Essex Institute, XXIII, pp. 12-16, 1891. 
SAug. F. Foerste: Proc. Boston Soc. Nat. Hist., XXTV, pp. 261-263; 1889. 
