isons 
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Sir W. E. Logan on the age of the Quebec Rocks. 105 
ORTHISINA FESTINATA is about the size of the well known O. 
Verneuli. Externally it has more the aspect of a Trenton lime- 
stone fossil than that of a Primordial form. The casts of the in- 
terior however show that the dental plates of the ventral valve 
are totally absent, while in the species of the upper part of the 
Lower Silurian they are largely developed. This difference is 
80 great that some naturalists would make a new genus for the 
reception of this species, 
resembling a curved hollow cylinder narrowed to a point and 
closed at one end. This species occurs in the limestone of Belle 
Isle and also in rocks which seem to be the bottom of the Cal- 
ciferous sandrock at the Mingan Islands. 
ALTERELLA. I have proposed this genus for the reception 
of some species of small conical fossils com 
‘ow sheaths inserted one within the other. They resemble Zen- 
lished by the Geological Survey. (NEW SPECIES OF LOWER 
SILURLAN Fossizs, By EK. Billings Montreal, Nov. 21st, 1861.) 
ae a een 
Ant. XIV.— Letter from Sir Wat. E. Loan, Director of the Cana- 
dian Geological Survey, on Sir Roderick Murchison’s reference to 
the determination of the age of the Quebec Rocks. 
; Montreal, November 27, 1861. 
0 the Editors of the American Journal of Science: tae 
t Strs——In his address to the Geological Section of the 
= lane of the British Association, Sir Roden Murchison 
AM. Jour. Scl.—Srconp Sens, Vou. XXXII, No. 97.—Jan., 1862. 
; ~ 34 oat 
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