. 
5 The American Geologist. January, 1892 
the Marcellus shale, thus making it equal to Formations VIII, 
IX and X of the Pennsylvania column. The term Catskill group 
appears for the first time in Vanuxem/‘s* final report, where it is 
used to designate the rocks at the top of the Devonian, which 
are regarded as fully equalling in importance the underlying 
Chemung and Hamilton, forming his Erie division; so that the 
Krie and Catskill are equivalent to the VIII and IX of Rogers. 
No line of demarcation between Erie and Catskill was determined. 
Hall’st final report appeared one year later and contained the 
grouping which has remained unchanged: 
Old Red sandstone or Catskill. 
Chemung group. 
Portage group. 
Fifteen years later appeared the final report on the Geologyt 
of Pennsylvania, in which Chemung and Portage are called Ver- 
gent, and the Catskill is the Ponent of the palzozoic column. 
This report took shape long after the original corps of observers 
had been scattered and the field-note books were not worked up 
in all cases by those who had made them; so that the statements 
are sometimes obscure and local details are too often perplexing 
to readers not familiar with the ground. Little additional sys- 
tematic information became available after the publication of 
Rogers’ final report until the results obtained by the Second 
(reological survey of Pennsylvania became known, 
The studies by assistants on the Second Pennsylvania Survey 
were very much in detail, owing largely to the immense economic 
importance attaching to the upper portion of the Devonian col- 
umn. But this detailed study, though leading to close concord 
in record of stratigraphical work, has led to wide difference of 
opinion in respect to lines of separation between the groups. As 
the area of Pennsylvania is large, great variations exist in 
physical characters of rocks and in vertical distribution of fossils, 
so that difference of opinion arose to a greater or less degree 
respecting the limitations of every group: but the difference is 
especially noteworthy in the case of Catskill and Chemung, for 
one observer carries the upper boundary line of Chemung almost 
2,000 feet further up in the column than is done by another. 
*Geology of New York, part III, Albany, 1842. p. 12. 
tGeology of New York, Part IV. Albany, 1848 pp. 18-19. 
rGeology of Pennsylvania, H. D. Rogers, Philadelphia, 185s. 
