Bar veil — Groivth of Knoivledge of Earth Structure. 151 



weigh facts and interpret them Edward Hitchcock 

 showed much more insight than H. D. Rogers, while in 

 the philosophic and comprehensive aspects of the subject 

 J. D. Dana far outranks him. 



H. D. Rogers in his first report on the geological sur- 

 vey of New Jersey, 1836, recognizes that the Cambro- 

 Silurian limestones (lower Secondary limestones) were 

 deposited as nearly horizontal beds and the ridges of 

 pre-Cambrian gneiss (Primary) had been pushed up as 

 anticlinal axes (p. 128). He also clearly recognized the 

 distinction between slaty cleavage and true dip as shown 

 in the Ordovician slates (p. 97). Between 1836 and 1840 

 he had learned a great deal on the nature of folds as is 

 shown in his Pennsylvania report for 1839 and the struc- 

 ture sections in his New Jersey report for 1840. 



R. C. Taylor, who had now become president of the 

 board of directors of the Dauphin and Susquehanna Coal 

 Company, published in the Journal in 1841 (41, 80) an 

 important paper entitled "Notice of a Model of the 

 Western portion of the Schuylkill or Southern Coal 

 Field of Pennsylvania, in illustration of an Address to 

 the Association of American Geologists, on the most 

 appropriate modes for representing Geological Phe- 

 nomena. " In this paper he calls attention to the value 

 of modeling as a means of showing true relations in three 

 dimensions. He condemns the custom prevalent among 

 geologists of showing structure sections with an exag- 

 gerated vertical scale with its resultant topographic and 

 structural distortions. Taylor was widely acquainted 

 with the structure of Pennsylvania, Maryland, and Vir- 

 ginia. 



Nature of Forces Producing Folding. 



In 1825 Dr. J. H. Steele sent to Professor Silliman two 

 detailed drawings and description of an overturned fold 

 at Saratoga Lake, New York. As to the significance of 

 this feature Steele makes the following statement (9, 3, 

 1825) : * 



"It is impossible to examine this locality without being 

 strongly impressed with the belief that the position which the 

 strata here assume could not have been effected in any other 

 way than by a power operating from beneath upwards and at 

 the same time possessing a progressive force ; something analo- 

 gous to what takes place in the breaking up of the ice of large 



