Chap. XVIII.] 
PETKOLEUM IN NORTH AMERICA. 
443 
all the seas of Palaeozoic times, even the very last of them, had a very- 
great extension, and were inhabited by similar groups of animals over 
enormously wide areas. 
In concluding the Twelfth Chapter I stated that much important information 
respecting the geological position of the great oil-bearing formations of North 
America would be communicated in the sequel ; and, thanks to Dr. Sterry Hunt, 
I now offer a view of these deposits and their origin which will, I doubt not, 
be as new to many of my readers as it was to myself when I first perused that 
excellent work ' The Geology of Canada.' 
Petroleum in North America. — Petroleum occurs at several horizons in the 
great Palaeozoic basin of North America. The lowest source is in the Lower 
Silurian limestones of Trenton, which are more or less oleiferous from Quebec 
to the Manitoulin Islands in Lake Huron, and thence to Chicago, and southwards 
as far as Kentucky and Tennessee. The great overlying mass of sandstones, 
shales, and dolomites which make up the remainder of the Silurian system is 
destitute of petroleum ; but the Corniferous or Lower Devonian Limestone is, 
like that of Trenton, oil-bearing, and furnishes the petroleum of the south- 
western peninsula of Canada, and of some parts of Kentucky, in both of which 
regions the wells are often sunk directly into this limestone. In the interme- 
diate region it is generally overlain conformably by higher Devonian and Car- 
boniferous rocks, in both of which, however, important oil-wells are found. 
Those of "Western Pennsylvania are sunk in the shales and sand-rocks of the 
Upper Devonian. 
The observations of that accomplished mineralogist and geologist Dr. Sterry 
Hunt, as recorded in the ' Geology of Canada,' pages 522-525, and in Silliman's 
' American Journal ' for March 1863, show that the oil in the two limestone 
formations above mentioned could not have been introduced by a subsequent 
process, but must have been indigenous to certain beds of the rock. When 
these limestones, or their overlying strata, are more or less disturbed from their 
horizontal position, the petroleum escaping from these beds finds its way to the 
surface, or else accumulates in the fissures of the anticlinals where these are 
stopped or closed by overlying impermeable clayey strata. In some cases the 
Quaternary gravels, covered by clays, which overlie these Palaeozoic rocks, serve 
as reservoirs for the oil, and constitute what are called surface-wells. It is con- 
sidered probable by Dr. Hunt that the oil-fissures in the Devonian sandstones of 
Pennsylvania may have been filled from the underlying limestone formation, 
inasmuch as there appears to be as yet no evidence that oil is indigenous in 
these Upper Devonian strata. The great conglomerate at the base of the coal 
in Kentucky appears to hold, according to Lesley, indigenous petroleum. Apart 
from this, however, it would seem that this substance belongs to the pure or 
non-magnesian limestone formations of the Palaeozoic series. The Lower Car- 
boniferous Limestone of Kentucky is, according to Lesley, oil-bearing ; and it is 
ceived geographical name ' Permian,' is wholly Let me add that it will be a subj ect of great 
inapplicable in America, where the formation interest to me, should the Permian zone be found 
(at Nebraska City) is a Monas, or one calcareous to range northwards through the United States into 
mass. In truth, the group varies from a single to the British territories. For certain small Producti, 
a quadripartite diveision, according to the country and other fossils in a magnesian limestone brought 
examined, and thus the simple geographical term home by Sir John Richardson in his early travels 
4 Permian ' is suited to embrace all such varia- with Franklin, and which have been mislaid, were, 
tions, whilst that of By as, intended by M. Marcou I believe, Permian ; and in this case, a zone of that 
to indicate some relation to the Trias, is, by virtue age may be said to extend at intervals from Mexico 
of its fauna, entirely separated from that Secon- even into the Arctic regions watered by the great 
dary group. Mackenzie Eiver. 
