77 
Mohawk river. The specimen in my cabinet, from 
which our cast was made, is from that place. 
The Cryptolithus Tessellatus occurs also in the - 
limestone which, according to Dr. Bigsby, overlays 
the sandstone in the island of Montreal. At most of 
its localities, it is associated with the Isotelus, the 
Calymene, and with several species of Asaphus. The 
Cryptolithus, whichis entirely destitute of eyes, being 
thus found with the oculiferous species, is an inte- 
resting fact, and controverts the opinion of Professor 
Wahlenberg, that the trilobites, which are without 
eyes belong to a geological epoch more ancient than 
those which are furnished with oculiform tubercles. 
That.organic remains furnish us with the most satis- 
factory evidence of the identity or dissimilarity of 
certain formations, is a disputed point with some — 
geologists* It cannot reasonably be doubted, that 
new and isolated facts have been made the basis of a 
too hasty generalization. On this subject Count 
Rasoumowsky makes the following remarks:—* Les 
divers gisemens des Trilobites ne me semblent pas 
non plus pouvoir ¢tre déterminés avec quelque pre- 
cision. M. Brongniart parait admettre que les trilo- 
bites aveugles ne se trouvent que dans de tres an- 
ciennes formations dans des schistes et des calcaires 
de transitions; mais nous avons donné la descrip- 
tion d’un trilobite [without eyes] des bords de la 
Yaousa prés de Moscow, Monsen certaine- 
menigpas aux formations de transition, ce qui me 
* See Eclectic Review, for July, 1832. 
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