150 Barrell — Groivth of Knoivledge of Earth Structure. 



America. The early examples of structure were sections 

 drawn with exaggerated vertical scales and those of 

 Maclure do not show detail. 



Recognition of Appalachian Structures. 



Following the founding of the Journal in 1818 there is 

 observable a growth in the quality and detail of geologi- 

 cal mapping. Dr. Aiken, professor of natural philosophy 

 and chemistry in Mt. St. Mary's College, published in the 

 Journal in 1834 (26, 219) a vertical section extending 

 between Baltimore and Wheeling, a distance of nearly 

 250 miles, on a scale of about 7 miles per inch. The suc- 

 cession of rocks is carefully shown and the direction of 

 dip, but no attempt is made to show the underground 

 relations, the stratigraphic sequence, and the folded 

 structures which are so clear in that Appalachian section. 

 The text also shows that the author had not recognized 

 the folded structure. Furthermore, where the folds 

 cease at the Alleghany mountain front, the flat strata are 

 shown as resting unconformably on the folded rocks to 

 the east. 



R. C. Taylor, geologist, civil and mining engineer, was 

 from 1830 to 1835 the leading student of Pennsylvanian 

 geology as shown by the publication in 1835 of four 

 papers aggregating over 80 pages in the Transactions of 

 the Geological Society of Pennsylvania. His work is 

 noticeable for accuracy in detail and no doubt was influ- 

 ential in setting a high standard for the state geological 

 survey which immediately followed. 



H. D. and W. B. Eogers have been given credit in this 

 country, and in Europe also, as being the leading 

 expounders of Appalachian structure. Merrill speaks of 

 H. D. Rogers as unquestionably the leading structural 

 geologist of his time. 8 To the writer, this attributed 

 position appears to be due to his opportunities rather 

 than to scientific acumen. The magnificent but readily 

 decipherable folded structure of Pennsylvania, the rela- 

 tionships of coal and iron to this structure, the consid- 

 erable sums of money appropriated, and the work of a 

 corps of able assistants were factors which made it com- 

 paratively easy to reach important results. In ability to 



8 G. P. Merrill, Contributions to the History of American Geology. 

 Eeport of the U. S. National Museum for 1904, p. 328. 



