AMERICAN GEOLOGY DECADE OF 1840-1849. 397 



The nature of the country, its strata, and fossils were described in 

 detail. The most interesting- part of the paper, from our standpoint, 

 lies in his remarks on the theory of elevation and the age of the 

 deposits. He regarded the formation of each Tertiary division and 

 the final annihilation of its fauna as a very gradual operation, taking 

 place in quiescent waters and having no connection with volcanic 

 agencies or any violent movements of the earth's crust, but merely 

 depending on changes of temperature. 



In discussing the effects of these temperature changes he showed 

 some peculiar ideas regarding the conductivity of rock musses and the 

 effects of cooling. The cold penetrating deep into the igneous rocks 

 beneath the surface, he thought, would result in a maximum amount 

 of crystallization and expansion," producing thereby a slight eleva- 

 tion of the crust. Since the cold penetrated gradually, he argued that 

 the elevation would also be gradual, more appreciable, of course, dur- 

 ing epochs of unusual cold. In brief, erustal elevation, he would 

 have us believe, was induced not by volcanic agency, but by "the all- 

 powerful and pervading influence of crystallization in the primary 

 rocks. " In this he followed what he calls the "sublime" theory 

 advanced by Vanuxem. The idea that the abrupt change in the char- 

 acter of the animal life at the close of each geological epoch by a sud- 

 den fall of temperature was, however, avowedly the theory of Agassiz. 



In connection with work pertaining to the Liberian Colonization 

 Society, in 1845-1848, David Christy traveled extensively throughout 

 the eastern and middle United States. Being a man of active mind 

 David Christy's and with a love for the sciences, he made many geo- 

 obse°rvaUons, logical observations which were first embodied in a 



series of letters to Dr. John Locke and published in 

 the Cincinnati Gazette. These were afterwards issued (in 1848) in 

 pamphlet form, some 70 pages, with 5 plates of fossils and three geo- 

 logical sections: the first from Mine La Motte and Pilotknob, Mis- 

 souri, to Hollidaysburg, Pennsylvania; the second from Lake Erie to 

 Pensacola Bay, and the third from Richmond, Indiana, through 

 Oxford, Ohio, to Beans Station, Tennessee. 



It is impossible to say what portion of the information given in 

 these letters can be claimed to be strictly the result of original inves- 

 tigation or observation. As stated by Locke in his introductory note, 

 he "referred the geological formations to the Blue Limestone of Cin- 

 cinnati as a kind of zero, informing us whether the rocks at any place 

 are above or below that zero." Locke further states that he knew of 

 "no other individual who has actually drawn approximate sections of 

 the strata from the Atlantic to Iowa and from Lake Erie to the Gulf 

 of Mexico; most of this work being the result of his own observations." 



In a letter addressed to M. de Verneuil in 1847, relative to the 



" As a matter of fact, crystallization in a rock magma would result in contraction. 



