320 On the Geology of the Northwestern Regions of America. 
somewhat more than 1500 miles. Such an enormous extension 
of crystalline and eruptive rocks, nowhere assuming the character 
of a mountain district, isa remarkable example of the tranquil 
operation of an upheaving foree exerted over an immense area, 
yet with a limited and regulated intensity, and a constancy of 
direction which render it worthy of attention, not only as a 
striking geological phenomenon, but as serving, perhaps, to throw 
some light on the dynamical conditions under which those vast 
sedimentary deposits which have excited the astonishment of 
geologists in America from their unparalleled extension have been 
originally upheaved. 
It may be mentioned also as another remarkable circumstance 
Mountains, that all the great lakes of America are found. If we 
regard Lake Erie and Lake Michigan as expansions respectively 
of Lake Ontario and Lake Huron (being evidently component 
parts of the same lake-basins), we shall find the following series 
of great lakes—Lake Ontario, Lake Huron, Lake Superior, Lake 
Winipeg, Athabasca Lake, Great Slave Lake, Marten Lake, and 
Great Bear Lake, succeeding one another in a NNW direction 
along the line of fracture, and invariably, bounded to a greater or 
less extent on one side (generally the northern or eastern) by 
crystalline rocks, and on the opposite side by limestones and other 
secondary formations; the northern coast-line being moreover 
indented nearly in the same general bearing by Coronation Gulf, 
where, as already stated, the line of crystalline rocks terminates. 
It is to be observed, however, that the rivers connecting these 
lakes run generally wholly in one formation or in the other. — 
Silurian Basin of Hudson’s Bay.—The granitic tract Just 
described is bounded to the eastward by a narrow belt of lime- 
stone, beyond which there is a flat swampy and partly alluvial 
district, forming the shores of Hudson’s Bay. The west coast 0 
the bay is everywhere extremely low, and the depth of water 
decreases so gradually on approaching it, that in seven fathoms of 
water the tops of the trees on the land are just visible from 4 
ship’s deck. Large boulder-stones are scattered over the beach, 
and sometimes form shoals as far as five miles from shore. A 
ac 
containing boulder-stones. Beyond this occurs an extensive de- 
posit of limestone, completely encircling Hudson’s Bay, a” 
following the course of the crystalline rocks to the extreme limit 
of our researches in the Arctic S : : 
ciliata 
