[Amr] GEOLOGY OF SOME CITIES IN EASTERN CANADA 161 
collections. The writers, above mentioned, have all concurred in 
ascribing the age of these limestones to the Lower Helderberg forma- 
tion which constituted the summit of the Silurian system in the New 
York succession. The presence of such forms as Favosites, like I’. 
Helderbergiv, Hall, of several other corals and a number of Bryozoa, be- 
sides an abundant brachiopodous fauna including :—Orthis probably 
Orthis (Rhipidomella) eminens, Hall, Orthis (Rhipidomella) oblata, Hall, 
and Orthis, sp. resembling somewhat Orthis (Orthostrophia) stropho- 
menoides, Hall, Strophonella punctulifera, Strophodonta varistriata, 
Leptæna rhomboidalis, Wilkens, Spirifer cyclopterus, Hall, Atrypa 
reticularis, Pentamerus (Sieberella) galeatus, Dalman, and ÆZatonia 
sinuata, Hall, indicate a Lower Helderberg fauna. 
All these occur in only a few cubic feet of limestone as preserved 
at the locality mentioned, and their occurrence is probably due to the 
protection afforded by the presence of the numerous intersecting dykes 
of volcanic rocks in post-Silurian times. 
Other outcrops of similar patches of limestone belonging to the 
Silurian system are reported to exist along the face of Belceil and other 
voleanic peaks in this district. This isolated outerop of Silurian strata 
points a time when the Lower Helderberg sea extended northward from 
New York State as far as Montreal and probably extended from thence 
in an easterly direction along the present valley of the St. Lawrence, 
as far as Gaspé Peninsula, where deposits of practically the same age 
occur. 
This also points to the enormous amount of denudation and erosion 
which must have taken place in this portion of North America in post- 
Paleozoic times, inasmuch as there practically remains but a few cubic 
yards of what was once an extensive and well-developed geological forma- 
tion, stretching over hundreds of square miles. The nearest outcrop of 
Silurian rocks are the so-called red shales and marls of the Medina 
described and mapped by Sir William Logan south of Lake St. Peter, 
some forty miles to the east of Montreal. 
THE DEVONIAN SYSTEM. 
The Hamilton formation (?).—On St. Helen’s Island there occur 
breccias and voleanic agglomerates in which are found pebbles of lime- 
‘stone occasionally holding fossil organic remains which appear to point 
to an horizon in the Devonian not far from the Hamilton formation. 
These fossils are embedded in a matrix of light or yellowish-gray im- 
pure limestone, cemeted by a ferruginous and siliceous matrix, probably 
associated with voleanic ash-materials. From an examination of some 
