NATURAL SCIENCES OF PHILADELPHIA. 441 



downward or upward in order that it may admit of explanation. 

 Thus the finding of a single small shell imbedded in the crest of 

 a lofty range of interior mountains of which the base, flanks, and 

 comb prove to be made up respectively of the same persistent 

 strata, and the identification of this shell with an exclusively 

 marine species, require the conclusion that the whole of this lofty 

 range was once under an ocean whose level was thousands of feet 

 lower, and whose margin is now thousands of miles away. 



The greatest conquests of the mind over large areas will never 

 result from the direct application of the physical power of man to 

 overcome the obstacles which stand in the way of their realization. 

 The inductive plan, though never leading to certainty, outstrips 

 by leagues the snail's pace of actual demonstration. A good 

 consulting geologist will furnish information in a few weeks as to 

 the number of tons of valuable mineral on a property, which will 

 enable a company to organize, start its business, grow rich, and 

 bequeath its industry to a new generation before a theory-hater 

 could sink the number of trial shafts sufficient to demonstrate 

 to a certainty that the deposit was continuous. And thus what 

 with reports already made on adjoining properties, science goes 

 on triangulating, as it were, from one area to another, till the belts 

 of country which are unknown as to their general possibilities 

 become very few and isolated. 



But there are such belts aggravating broad belts of well-settled 

 country which occupy in the geological finished map the positions 

 which used to be held by the ''Great American Desert," the central 

 parts of Africa, and the high lands of the Mountains of the Moon 

 or the Himalayas in our school geographies. 



It is not so long ago since it was taught in school-books that 

 the bottom of the ocean was a great floor of fine sand. The writers, 

 following each other, had observed the deposition of suspended 

 substances in the deltas and along the sea coast, and observing 

 the currents of the sea, and forgetting that the immense organic 

 life of the ocean must find a final resting place, had dusted the 

 whole ocean with the sand of the sea-shore but without its shells. 



Such an area is the Mesozoic red sandstone of the Atlantic 

 States. It sweeps upward from Virginia to New York, and exists 

 in North Carolina and Connecticut, appearing eveiy where (except 

 in N. C.) under a provoking uniformity of condition, and shut- 

 ting out our view from the underlying strata, and the part they 

 play in connecting the paleozoic series east and west of it. Singu- 

 larly enough, a large fraction of the American geologists who have 

 made themselves distinguished have passed or are passing their 

 lives upon it; and yet we know next to nothing about it. 



" If the Mesozoic shales only could be removed l'ike the lid of a 



box, what light would it not throw upon the structural riddles !" 



has been thought or expressed by every geologist. Here is a 



case where the ordinary methods of stratigraphy will not help us. 



29 



