GEOLOGICAL SURVEY OF THE TERRITORIES. 377 



coal, the equivalent of the mammoth vein of Pennsylvania, which 

 averages eight to ten feet in thickness, is found over the whole extent 

 of the coal measures of Ohio, Kentucky, Indiana, and Illinois, measur- 

 ing from four to eight feet. So immense, indeed, are the riches of 

 the American coal-measures, that in their conception of the future devel- 

 opment of our human race, geographers, historians, philosophers, agree 

 in this idea : that in the United States we have, especially in our coal 

 deposits, the elements for the greatest and most perfect development 

 of the human race. 



And what is petroleum or mineral oil, too, which is now entering in our 

 civilization, if not as one of its essential elements, at least as one of its 

 potent auxiliaries? It is, like coal, the result of slow maceration of 

 plants ; with this difference, that in the formation of the coal, the plants 

 which entered into the composition of the matter were woody or fibrous, 

 and the woody tissue cannot be destroyed by the slow process of combus- 

 tion no more than it is in burnt charcoal. The plants which concurred 

 to the formation of petroleum were sea-weeds or marine plants. These 

 have no fibers, no wood in their tissue, which is merely cellular ; and 

 in their decomposition all trace of this tissue has been destroyed, and 

 pure bitumen preserved, either by impregnation of shale or sandstone, 

 &c, or by accumulation in subterranean cavities. It is to fossil plants 

 also that we owe the explanation of this remarkable process of miueraliza- 

 tion. Deposits of oil are especially found in strata of the Upper Silu- 

 rian and the Lower Devonian, and always in connection with shale or 

 limestone, which contain in great quantity petrified remains of fucoids 

 or marine plants. The conditions bringing up an exuberance of vege- 

 tation were already at work before the carboniferous epoch ; their action 

 resulted in the production of an immense marine vegetation. As nature 

 does nothing in vain, as she takes care of all its materials and uses them, 

 to the minutest debris, she took the bitumen away and preserved it in 

 cavernous recesses for future use. By the discovery of our deposits of 

 petroleum we have learned what had been done with the superabundant 

 production of marine plants in our old geological epochs. Coal and 

 petroleum are found in all the geological formations. But since the coal 

 era the deposits of these matters have become of comparatively rare 

 occurrence, and of far less importance, their value being diminished as 

 much by the reduction of their areas as by the inferior quality of their 

 products. They now take a nominal and far more modest place in the 

 harmony of our earth's surface. 



ON THE DISCORDANCE IN THE CHARACTERS OF EUROPEAN AND AMER- 

 ICAN FLORA AT THE TERTIARY AND CRETACEOUS EPOCHS. 



Since the first appearance of land vegetation upon the surface of our 

 earth, what we know of it by fossil remains seems to indicate for our 

 country a precedence in time in the development of botanical types. 

 Large trunks of coniferous wood are already found in our Devonian 

 measures, while analogous species are recorded as yet only in the car- 

 boniferous measures of England. Though the analogy of vegetation 

 between the, flora of the coal measures of America and Europe is evi- 

 dently established by a number of identical genera and species, we have 

 nevertheless some types, like the Paleoxiris, which are considered as char- 



