AMERICAN GEOLOGY DECADE OF 1830-1839. 355 



Washington on the Potomac, he suggested, was probably contempo- 

 raneous with the London clay, i. e. Eocene. 



The cause of the change in the character of animal life between rocks 

 belonging to the different animal horizons, was regarded by Conrad as 

 due to climatic changes. ""Periodical refrigeration alone can explain 

 the sudden extinction of whole races of animals and vegetables." 



It is well to note that in his Geological Report for the State of New 

 York, Conrad recognized the fact that in the earlier eras of our planet 

 the temperature was uniform and the seas comparatively shallow. 

 Hence, he thought, in the older rocks we should expect to find organic 

 remains belonging to one group of species over the whole globe. 

 Deep erosion and greater variation of temperature had caused more 

 uncertainty in the Upper Tertiary formations. 



In connection with Conrad's work, it may not be out of place to note 

 that Prof. J. L. Kiddell this same year described the surface geology 

 of Trinity County, Texas, and, basing his determinations mainly on 

 the beds of lignite there found, put down the prevailing sandstone 

 as Tertiary. 



Incidentally, also, it may be noted that during 1840 Mr. James T. 

 Hodge made a trip through the eastern portion of the southern Atlan- 

 tic States and made extensive collections of fossils, which were turned 

 over to Conrad for identification. Hodge's notes, as published in the 

 Transactions of the Association of American Geologists, contain little 

 of geological value, but the list of fossils comprised some 134 species, of 

 which 32 were then new to science. All were of Tertiary age. 



Conrad was born in Philadelphia in 1803, and from early youth 

 showed a decided taste for natural-history studies, though for a time 

 following the calling of his father — that of a publisher and printer. 

 The work noted on page 306 was his second of geolog- 

 sketch of Conrad. ical importance, and was preceded also in 1831 by a 

 paper on American marine conchology. Of his subse- 

 quent writings on conchology, paleontology, or general geology upward 

 of twenty related to the Tertiary, and it is upon these that his fame as a 

 geologist chieily rests, though in addition he described the fossils col- 

 lected by the Wilkes exploring expedition, by Lieutenant Lynch's 

 expedition to the Dead Sea, by the Mexican boundary survey under 

 Lieutenant Emery, and was first geologist and then paleontologist 

 to the New York State survey. 



Personally Conrad was peculiar. 



He wrote his letters and labels frequently on all sorts of scraps of paper, generally 

 without date or location. He was naturally careless or unmethodical, and his cita- 

 tions nf other authors' works can not he safely trusted without verification, ami are 

 usually incomplete. He had a very poor memory, ami on several occasions has 

 redescribed his own species. This defect increased with aye, and, while no question 

 of willful misstatement need arise, made it impossible to place implicit confidence in 

 his own recollections of such matters as dates of publication. (Dall.) 



