THE CARBONIFEROUS SYSTEM. 105 



above the ocean level, and contained an adequate supply of crystalline 

 quartz. Tracing out the limits of the Palaeozoic 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 500 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 Palaeozoic sediments, 

 the uppermost layers of which, at the time the Conglomerate was formed, 

 were unconsolidated organic or mechanical mud. 



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- 



