320 
PALAEONTOLOGY OF NEW-YORK. 
For these reasons, and because a careful examination of the structure of this part of the 
country has shown a clear connexion of the rocks on the east and west side of the Hudson- 
river valley, I have considered it my duty to unite these fossils with those found in other 
localities of the Hudson-river group. Whatever future investigations may develope, we 
have at present no sufficient evidence for regarding the rocks on the east side of the Hudson 
river as distinct from those on the west side ; since they are visibly connected, and the 
undulated and plicated structure and partial alteration commences on the west side of the 
river, while the fossils still retain their form and unequivocal character. Those who in¬ 
vestigate the subject should remember, also, that the discovery of a few species in the 
altered shales on the east side of the river is not decisive of a different age of the strata, 
while so many unequivocal forms of the unaltered rocks on the west side appear in the 
same connexion. A careful search conducted in any part of these strata, both in the dis¬ 
turbed and undisturbed regions, will lead to the discovery of many new species, which is 
likewise true in other formations. 
I conceive, however, that it is unnecessary, in this place, to enter into detail regarding 
the geological structure of this part of the country. This will appear in an introduction to 
the work, with sections showing the continuation of the formations eastward, and their 
gradual metamorphism which increases with their greater disturbance. 
