[MATTHEW] NOTES ON CAMBRIAN FAUNAS, No. 12 53 
In an earlier part of this paper the writer has called attention to 
the independence of the faunas of the Atlantic coast from those of 
the interior of North America and would suggest as an explanation 
of this difference the existence of a land barrier along the Appalachian 
ridge, dividing the continental interior from the “continental shelf,”’ 
spread out along the continental margin. This view was less dis- 
tinctly presented in the author’s presidential address to Section IV 
of this Society in 1891-2, based chiefly on the distribution of the Cam- 
brian faunas from Europe toward North America. 
As a further hypothesis collateral to that advanced in the address 
above referred to, he would now postulate the existence even in that 
early time (the pre-Cambrian) of a continental ridge that formed a 
barrier to the free mingling of the living forms which inhabited the 
oceans even before the Cambrian types had an existence. The dif- 
ferences between the species that inhabited the Atlantic coast in 
Cambrian time from those whose remains are found in the areas west 
of the Alleghanian ridge (including the coast of Labrador) is so marked, 
that they must have been kept apart by some physical barrier, whether 
difference of marine temperature, or an actual land barrier matters 
not, for the differences in the several faunas are convincing, that a 
barrier existed. 
If we postulate the presence of a deep and broad abyss off the 
Atlantic coast in this early time, filled with icy and therefore dense 
water as now, and assume that this mass of cold water was con- 
stantly weighing down the subjacent part of the earth’s crust, and de- 
pressing it, while the summer sun annually expanded the adjoining 
land, there would bea tendency in the continental border to rise and 
with the annual cooling to contract again and form folds of the rocks 
of the continental borders on a large scale; thus in winter and summer 
there would be a constant tendency to change in the continental border. 
Meanwhile the permanency and dead weight of the dense crust at 
the ocean bottom, to the eastward, and its overburden of chilled 
ocean water would exert a constant pressure on the sea-margin part 
of the crust, causing a thrust from the sea upon the land; hence we 
find from time to time periods when folded continental masses rose 
parallel to the coast: such a change happened in Ordovician time and 
again in the Devonian, and was very marked in Pennsylvania, &c., 
and in post-Carboniferous time. Even as late as the post-Pleiocene 
time there are evidences that such pressure was exercised in a small 
scale in the rocks that form the St. John basin of Cambrian rocks. 
The existence of a pre-Cambrian ridge shows that similar forces were 
at work in pre-Cambrian time and later in thrusting out the effusives 
that are so marked a feature of the Basal deposits of this region in 
