Review of Recent Geological Literature. hi 
Their age is approximately the age of the gravel. They 
cannot be older, they may be younger. If the gravel is Col- 
umbia in age then the streams date from the close of that pe- 
riod or later. The question arises, could the streams have 
trenched such deep valleys and so extendedly contested the di- 
vide since Columbia time? We find the erosion in southeast- 
ern New Jersey of a less mature character. We tind the Pen- 
sauken and Jamesburg gravels made up of material which 
must have been furnished them by streams draining this 
plateau. 
The red shale of the Newark, disintegrated gneiss, granite, 
trap, geirnetiferous crystalline schists and gabbro (the Bran- 
dy wine, Naaman, and Crum creeks flow across gabbro areas) 
and rounded fragments of ironstone would be furnished abun- 
dantl^y by just such streams as the creeks described above, 
eroding first the Bryn Mtuvr gravel, then the crystalline 
schists and igneous rocks of the plateau. 
These facts seem to concur in precluding the Quaternary 
age of the gravel. 
It is perhaps not possible to determine the age of a drain- 
age system with a degree of accuracy sufficient to distinguish 
between a late Mesozoic or an early Tertiary origin. On the 
other hand, the stream history furnishes no evidence against 
the Potomac (Mesozoic) age of the gravels. 
The other members of the Potomac series were in all prob- 
ability present in Pennsylvania and have either been com- 
pletely removed by an erosion, dating back to the dawn of the 
Tertiary, or will yet be discovered in small areas. 
That evidence of still more recent superficial deposits will 
be found seems highly improbable, hence the hypothesis has 
been stated that not very long after the deposit of the Bryn 
Mawr gravel the Pennsylvania!! plateau was permanently ele- 
vated and the present streams began their work of erosion. 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
The Underground Water of the Arlcansan Valley in Eastern Colo- 
rado. By G. K. Gilbert. (Extract from 17th Annual Report of the U. 
S. Geol. Survey, Part II.) This paper, which illustrates well the vari- 
ous excellencies which we have learned to expect from Mr. Gilbert, is 
