1022 Review of Repcrt C,, 2d Geol. Surv. of Penna, [O 
Mr. Hall's “ Notes,” 7. e., pp. 54 to 64, are brought 
sub-heading of Rogers called the “Southern Gneiss.” For 
reason neither the colored map (presumably that on wh 
error of the county map-maker, in continuing a water € 
very short distance too far along the Nottingham townsl 
der, was not “culpably copied”)! nor the reduced page 
placed opposite to Mr. Hall’s contribution, though he spea 
first sentence of “the accompanying map,” and he in 
present writer that this text was simply intended to explain 
and not to propound or support any theory whatever. 
plain in his pages, which are merely jottings from his field 
book. In his preliminary remarks he defines the areas 
map, which he has covered with certain symbols. All 
eral observations agree perfectly with those made by 
several years before Mr. Hall went to Chester county, p 
that the same limestone underlies parts of these township 
“not visible at the surface.” The rest of the “ Notes” a 
localities where Mr. Hall has observed, “ A. Laurentian 
“B. Sandstone and quartzite,” “C. Limestone,” “ D. F 
he was “ not able to convince himself of the true chi 
deposit.” While of E (mica schists) he frankly 
structure I found it impossible to reconcile the s 
this part of Chester county with that of Delaware 
means of the numerous outcrops of rocks along ne 
roads which cross the schist belt (if it be a belt), „e 
logical Survey. Thus Report C for 1874 hasa description and a 
(pp. 104 and 105) which seems to be conclusive as to their 
_ cludes, “ both the analyses tend to support the view that the mii 
which give the unctuous feel and pearly lustre to the schists belong to 
ite group of the Margarophyllite section of hydrous silicates (Dan 
What makes this nomenclature the more unfortunate is, that: 
table tale rocks which are thus confounded with the larger zone 
an important but very small geographical part, 3 
1 See p, 10. The here of carelessness on the part i 
