No. 50.] 
347 
Thus it appears, that by excavations equal in the aggregate to 6^ 
miles, and an amount of 240 feet lockage, continuous lines of navigation 
through, and connecting these tv^o rivers, may be formed, equal in 
extent to 210 miles; and that this would be increased, probably, to 
more than 300, if we take into consideration the coasts of the lakes. 
Respectfully yours, 
FARRAND N. BENEDICT. 
Accumulation of the Materials composing the Potsdam 
Sandstone. 
This rock is thickest at the north, and becomes thinner, though not 
in regular gradation, as it extends southward. It therefore loses its 
importance in the latter direction. At Little-Falls it does not appear, 
but the succeeding rock, the calciferous sand-rock, rests immediately 
upon the gneiss. It may be inferred, therefore, that although there 
was an open sea, and materials were drifting in, yet, in consequence 
of the hardness and coarseness of the particles and masses, they were 
not in a condition to be transported far from the parent rock, but were 
deposited in shore or into an estuary, into which large rivers emptied 
their contents. It is a reasonable hypothesis, however, that those ri- 
vers which bore along the siliceous gravel composing this sandstone, 
might also transport calcareous and argillaceous matter at the same time. 
Those materials being soft, and partially soluble and miscible in water, 
would be transported far out to sea ; they would subside but slowly, 
and moreover the rock composed from them would be partly mechani- 
cal and partly chemical. It is evident that the finer the particles, the 
farther they would be transported. In the breaking up of siliceous rocks, 
though much would be hard and in masses, still, in the attrition to 
which those masses would be subjected, much would become fine and 
impalpable, and might be carried along with the calcareous matter. 
Such being the condition of things, we may consider the following 
as the natural results : 
All the coarse, heavy masses would be deposited as soon as the cur- 
rent ceased to act upon them. These would constitute the largest body 
of the abraded materials, and form the thickest portion of the rock. — 
They would be in the line of their origin, and would indicate the course 
of the current or river which transported them. The finer, siliceous 
