THE CARBONIFEROUS SYSTEM. — 105 
above the ocean level, and contained an adequate supply of crystalline 
quartz. Tracing out the limits of the Paleozoic seas and lands, we find 
that a portion of the Alleghany belt, and the Eozoic area in Canada, 
New York, and Michigan, were the only regions which satisfy the condi- 
tions. Here the metamorphic rocks are every where intersected by veins 
of quartz possessing essentially the same mineral characters with that 
which forms the pebbles of the Conglomerate. This, then, is the source 
from which the material was derived. Second, as regards the manner of 
distribution of this material, we find in the present epoch that sands 
and gravel beds are the natural products of the action of shore waves 
upon the land, and that, in many portions of the geological series, such 
beds of gravel and sand were formed by the extension of ancient sea 
beaches. If, therefore, this sheet of sandstone and Conglomerate were 
spread over a continent consisting of crystalline rocks, of which quartz 
formed an important part, we should need to go no further for an expla- 
nation of the phenomena than to suppose that an invasion of the sea had 
leveled down and comminuted such materials as were encountered by 
the shore waves; and of these the most resistant, and such as possessed 
the highest specific gravity, were accumulated in a sheet which measured 
the reach of the sea. But when we examine the area over which the 
Carboniferous conglomerate is spread, we find districts where it exhibits 
its maximum development and coarseness many hundreds of miles away 
from any possible source of supply; as, for example, in western Kentucky, 
where the Conglomerate is in places 250 feet in thickness, and where it 
was 000 miles from any outcrop of crystalline, quartz-bearing rock, at 
the epoch of its deposition. Between this district and the Eozoic high- 
lands, or the Blue Ridge belt, lie unbroken sheets of Paleozoic sediments, 
the uppermost layers of which, at the time the Conglomerate was formed, 
were unconsolidated organic or mechanical mud. f 
It has been customary to suppose that the material forming the Con- 
glomerate was washed down from the highlands of the continent, and 
* transported by rivers to the localities where it is found; but the difficul- 
ties in the way of the acceptance of this explanation seem to be insur- 
mountable. It is true that river currents have the power of rolling 
gravel and sand along the bottoms of the channels they traverse, even to 
a great distance from their sources; but no river action is adequate to 
explain the uniformity that marks the distribution of this great sheet of 
consolidated sand and gravel. Hence the approximate uniformity in 
thickness of the deposit, and its similarity of composition over all parts 
of the area it occupies, forbid the acceptance of river action as the agency 
of its distribution. Again, the action of narrow currents of water hav- 
