24 
PALAEONTOLOGY OF NEW-YORK. 
conglomerates described by Sir W. E. Logan in the Geological Survey of 
Canada. 
At the west and southwest the upper beds are often calcareous, with 
more rarely arenaceous and calcareous strata in the higher part of the 
group. The transition to the succeeding formation is always strongly 
marked ; and it is only in rare instances that we have seen beds of 
passage, with a few of lower species of fossils. 
In the very heterogeneous assemblage of materials and fauna which 
constitute the Medina sandstone and Clinton group of theNew-York series, 
we have an indication of the recurrence of the causes .which produced 
the Hudson-river group, operating apparently in conjunction with other 
forces, which have finally culminated in the Niagara group. The evidence 
of sudden alternation and violent change exhibited in the Clinton group 
in New-York, long made it a very difficult and unsatisfactory study. The 
mingled character of its materials, and the very evident relation of its 
fauna with both lower and higher strata, left the results quite uncertain, 
with a strong indication that there was something more to be learned 
concerning its relations with the preceding and succeeding formations. 
With this idea I have followed the line of its outcrop in Canada West, 
upon the islands of Lake Huron, along the shores of Green Bay, and 
through Wisconsin. Examinations in all these localities have afforded no 
additional information beyond what we possessed in New-York. While 
the Medina sandstone can be identified only in a few points, the Clinton 
group is more persistent; and with its soft shales and associated iron ores, 
its beds of sandstone and impure limestone, it is clearly recognized in the 
State of Wisconsin. The conditions of alternating sea and shallow water 
and shore seem to have prevailed over the entire extent; for in Wisconsin, 
the surfaces of some of the beds are marked by tracks and trails as in 
New-York*. The fauna of the more westerly localities has afforded a few 
# I have elsewhere shown the reasons for inferring that the beds with Pentamerus oblongus and 
P. Itzvis. in Great Britain, should be separated from the Caradoc sandstone; and I believe this view 
is generally admitted. As originally described, the Caradoc beds included species or their analogues 
which are, with us, unknown below the Clinton group; while the true Caradoc fauna corresponds to 
that of our Hudson-river group. 
