66 ROCHESTER ACADEMY OF SCIENCE. [Jan. II, 



ological characters of these strata change decidedly in the course of 

 not very considerable distances. Professor Williams in reviewing the 

 geology of this region has admirably stated this opinion in the follow- 

 ing language : " The fact seems to be, as we review the records of 

 the survey [Pennsylvania] that the data of lithologic character of 

 rocks and of the thickness of the deposits were so constantly variable 

 that the ' theory of persistent parallelism of strata' was little more 

 than a theory, the exceptions to which were as numerous as the illus- 

 trations. It was a cut-and-try system of matching together innumer- 

 able sections, made up of irregular combinations of shales, sandstones, 

 conglomerates, and limestones of various color, thickness and texture. 

 Whenever the gaps were over a mile or two long the adjustment of 

 the theoretical dip, a few feet more or less to the mile, would enable 

 the parallelism to fit any particular stratum in a given section. The 

 fact that those who showed evidence of having noted the fossils, 

 although they may not have identified them, were invariably nearer 

 right than those who neglected them, strengthens the belief that the 

 fossils, even in this case, were the most valuable means of corre- 

 lation." {') 



In reference to the stratigraphical geology of the Allegany region, 

 Professor Williams wrote me as follows, October 31, 1891 : " Regard- 

 ing the relations of the Richburgh sands and theOlean conglomerate, 

 I remember that at the time [when writing Bulletin No. 41 J the sta- 

 tistics were confusing. I was then inclined to the opinion that there 

 were very sudden changes in the neighborhood of the oil sands — 

 laterally — /. e. on passing across the strata horizontally ; and later 

 studies led me to consider the * theory of persistent parallelism of 

 strata' very unsatisfactory as a means of correlation. It may be 

 satisfactory, then the next half mile may give perfectly unsatisfactory 

 results. I think only the fossils can be depended upon and even 

 these must be examined as faunas as well as individuals, for obtaining 

 the best results in correlation." 



(i.) Bull. U. S. Geol. Surv., No. 80, pp. iii, 11; 



