of the Older Formations of the United States. 11 
except in a few instances, and even here they do not bear the 
marks of great perfection. Although one or two species appear 
in great numbers, they do not acquire that perfect development 
of form which they do farther west; as for example, Delthyris 
mucronata. As we go westward, however the Avicula, Cypri- 
cardia, &c., gradually diminish in numbers and the Brachi- 
opoda become far more numerous in species and abundant as 
individuals. 
This group, therefore, at the two extremes of the State, pre- 
sentsa very different lithological character, and an association of 
fossils so unlike, when the most common forms are considered, 
that they would scarcely be recognized as the same. In the 
western part of the State there seems to bea larger proportion 
of caleareous mud, and there are also immense numbers of 
corals which are not common in the eastern part of the State. 
"The lithological changes, here enumerated, are strictly in 
accordance with the common laws relating to mechanical de- 
posits. Ifthe source of this great group was in the east or 
south-east, the sandy matter would first fall to the bottom of 
the ocean in its transport, the fine mud would remain longer 
suspended, and its greatest development would only occur 
after the sandy deposit had begun to diminish; and such pre- 
‘cisely we find to be the actual condition. "The sandy matter 
diminishes, the finer particles only continue to be transported, 
and there becomes a gradually increasing admixture of finer 
mud. At length the finer siliceous portions are almost lost, 
. and finally too, the soft mud itself has all sunk to the bolt 
and the ocean beyond is clear — a deep blue sea. 
Now ìt is very natural to inquire (when we are able to ‘ace 
le almost uninterruptedly over more than a thousand 
i üfide-of extent, which must have been covered by an ocean,) 
what were the conditions of its bed? In what direction was 
the continent that bounded it, or theislands which raised them- 
selves above its surface? And what evidence have we, if any, 
of increasing depth. as we recede from that ancient shore ? i 
From the facts before. us it would appear, both from the na- 
