On the Boulders of Primitive Rocks found in Ohio, fyc. 293 



leys of rivers, and they are the only species which are round- 

 ed and smoothed by attrition. The largest mass that I have 

 seen, is not more than two feet in diameter ; the composition 

 is uniformly fine grained, principally of hornblende, and to 

 the naked eye the texture is apparently homogenous ; and 

 with a glass, the grains of feldspar and prisms of hornblende 

 are plainly distinguished. 



Is there any evidence, that similar minerals are in place 

 north of the great lakes ? If such evidence exists, as to all 

 of them, it would lay a foundation to conjecture, that they 

 all had the same local origin, but, if it exists as to a part only, 

 such conjecture would not be admitted, any more than it 

 would be reasonable to suppose, that all these boulders came 

 from Massachusetts, because a mass of granite is found in 

 the town of Randolph, Portage county, Ohio, identical in its 

 appearance with the granite, excavated at Rail hill, North- 

 ampton, Mass. ; or, because a mass of old red sandstone, ap- 

 parently like the old red sandstone that underlies Mount 

 Tom, is found in the neighborhood of the granite. 



If it were ascertained, that there existed a northern ridge, 

 composed of similar materials with the boulders, and the in- 

 termediate country were an inclined plain, descending to the 

 north western territory, the " impression 1 ' might be strong, 

 that the boulders came from that ridge, but it would not be 

 " irresistible," for we should still want a force adequate to 

 the removal of such ponderous masses. Could that force be 

 water ? To say, that an immense body of water was, at some 

 remote period, collected at or near the north pole, and that 

 it flowed over the north western territory, carrying with it 

 large masses of granite and depositing them, at an altitude 

 of one thousand one hundred and sixty-five feet above the 

 present surface of the Atlantic ocean, where some of them 

 now repose, would seem to be indulging something like the 

 visionary daring of Capt. Symmes. 



"It may be doubted whether the uniformity, order and 

 regularity of the general laws of nature, which have at any 

 time come within the limits of our observation, can warrant 

 a supposition, founded on such complete changes in the 

 mode of action."* It is incumbent on the supporters of 



* "Essay on the formation of Rocks," &c. by William Maclure ; Journal of 

 the Academy of Natural Sciences, vol. 1, p. 261. This essay ought not to be 

 mentioned without an acknowledgment — it is strikingly characteristic of its 

 author; its extensive and accurate research, its clearness, precision and truth, 

 are not more remarkable than its philosophic caution and invariable modesty. 



