66 Recent Literature. _ [January, 
2. “It is clear that the Potsdam sandstone was deposited on 
the third belt.” l 
This is not in conformity with numberless observations made 
in Adams, York, Lancaster and Chester counties as may be seen 
by consulting the maps and text of reports, C, CC, and CCC and 
of Chester county when it is published, as well as notes made b; 
Dr. Frazer in the company of Mr. Hall at Harper’s Ferry. i3 
3. “ But it is equally clear that the mica schists and gneisses 
are not found between the Primal and the rocks of the third belt.” 
This statement is inconsistent with a whole host of observations 
on the South mountain and in the counties named above as well 
as in Cumberland and Franklin. f 
4. “If the mica schists were older than the Potsdam, they must 
have been deposited up to a geographical line.” Not if there was 
a fault along the South Valley hill which diverged to the south 
slightly before reaching the eastern extremity of that valley. 
5. “ Even supposing a fault * * there would still be some 
remnants of these rocks in their normal position * * and | 
fragments * * entombed in the Potsdam,” &c. ae 
As to the first, abundant demonstration of it exists in the | 
counties above named, and that the second proposition is in ač- 
cordance with Mr. Hall’s observations is clear from the fact, that 
out of six specimens of his Potsdam or Edge Hill rock sent to | 
the laboratory for analysis, four were named by Dr. Genth and 
his son “ hydro-mica schist ;” which proves an abundance of that 
material in the rock. ee 
Space will not here permit a presentation of the reasons for the — 
opposite view, z. e., that the South Valley Hill rocks belong ġelow — 
the limestone. This one consideration may be, however, pre — 
sented that he who can, may accommodate it to Mr. Hall’s theory. 
In at least two places in Chester county limited areas of Lauren- 
tian rocks are observed to be in contact with the South Valley Hill ve 
schists (on this point Mr. Hall and Dr. Frazer are in accord). One — 
of these areas, near West Chester, is completely surrounded by 
them. The other forms a narrow tongue or peninsula in contact 
with them on three sides. Yet there is not a sign of any of thê 
thousands of feet of the Huronian, Potsdam or Limestone which | : 
ought to appear between them, according to Mr. Hall’s view. | 
The color scale on the large geological map which accompanies — 
Mr. Hall’s report, seems to the stranger not to agree with the — 
color as used on the map. On the former the intermediate 
Manayunk belt is designated by dark red, whereas on the map — 
this color seems to be given to the northerly Chestnut Hill group, 
and vice versa. ie 
The last forty pages contain the report of Dr. Genth on the | 
dolerites, mica schists, gneisses, granites and other rocks of the 
district, and constitutes a very valuable leaf in the still small bo 
of chemical lithology.—P. F. (tie tbo la 
ee 
