182 
ELEMENTS OF GEOLOGY. 
promontory called Selsea Bill, in which Mr. Godwin-Austeii 
found thirty-eight species of shells, and the number has since 
been raised to seventy. 
This assemblage is interesting because on the whole, while 
all the species are recent, they have a somewhat more south¬ 
ern aspect than those of the present British Channel. It is 
true that about forty of them range from British to high 
northern latitudes; but several of them, as, for example, Lii- 
traria rugosa and Pecten polymorphus^ which are abundant, 
are not known at present to range farther north than the 
coast of Portugal, and seem to indicate a warmer tempera¬ 
ture than now prevails on the coast where we find them fos¬ 
sil. What renders this curious is the fact that the sandy 
loam in which they occur is overlaid by yellow clayey gravel 
with large erratic blocks which must have been drifted into 
their present position by ice when the climate had become 
much colder. These transported fragments of granite, syen¬ 
ite, and greenstone, as well as of Devonian and Silurian rocks, 
may have come from the coast of Normandy and Brittany, 
and are many of them of such large size that we must sup¬ 
pose them to have been drifted into their present site by 
coast-ice. I measured one of granite, at Pagham, 21 feet in 
circurnfex'ence. In the gravel of this drift with erratics are 
a few littoral shells of living species, indicating an ancient 
coast-line. 
Glacial Formations in North America. — In the western 
hemisphere, both in Canada and as far south as the 40th 
and even 38th parallel of latitude in the United States, we 
meet with a repetition of all the peculiarities which distin¬ 
guish the European boulder formation. Fragments of rock 
have travelled for great distances, especially from north to 
south: the surface of the subjacent rock is smoothed, stria¬ 
ted, and fluted; unstratified mud or till containing boulders 
is associated with strata of loam, sand, and clay, usually de¬ 
void of fossils. Where shells are present, they are of spe¬ 
cies still living in northern seas, and not a few of them iden¬ 
tical with those belonging to European drift, including most 
of those already figured, p. 176. The fauna also of the gla¬ 
cial epoch in North America is less rich in species than that 
now inhabiting the adjacent sea, whether in the Gulf of St. 
Lawrence, or ofiT the shores of Maine, or in the Bay of Mas¬ 
sachusetts. 
The extension on the American continent of the range of 
erratics during the Post-pliocene period to lower latitudes 
than they reached in Europe, agrees well with the present 
southward deflection of the isothermal lines, or rather the 
