524 7 Recent Literature. [May, 
more probable to suppose that mention of them was in some way 
omitted in the course of arranging his MSS for the press.! They 
are marked in Frazer’s unissued map, which was colored in 1880, 
Mr. Rand is right, in a sense, in insisting that the outcrops of 
serpentine should be represented by detached areas rather than 
by a continuous line, and Mr. Hall himself has been a notable 
champion for this kind of geological Realism, but it may be car- 
ried too far, and if this system had been uniformly adopted by 
all geologists, no continuous structure of large areas would ever 
have been attained. In the present instance it is almost as much 
a matter of judgment as of observation where the limits of the 
separate serpentine areas should be placed, for if the surface be 
minutely examined and its indications alone regarded, each 
these areas will show numerous interruptions of a few feet or 
yards of continuity both witk and across the strike, where the 
serpentinous matter is replaced by clastic rocks. In fact, much 
of the area called serpentine has little to ally it to that mineral 
but its blasting influence on vegetation, the rocks being of the 
most heterogeneous and nondescript character. 
Mr. Rand complains that Mr. Hall makes no mention of the 
Potsdam sandstone which, following Rogers, he notes south as 
the South Valley hill, beyond the signalization of “ sandy beds. 
We think that Mr. Hall is entirely right in this, for the reason 
that the hypothesis that these beds of white sand near the King 
of Prussia, for example, may easily have resulted from the de- 
composition of any of a great variety of rocks not Potsdam of 
any other sandstones. It is true that it would not be difficult to 
uth ale 
ley Hill rocks here, than in joining the Potsdam and the j f the 
i . + . ii 
question it would simply shift a little to the wostward 4 
tersection of the valley axis and the line of fault, whic e 
supposes to bring up the lower series to the preset | 
The observation of the intersection of the Serpentine ye estiOg 
trap which has a more northerly trend in Easttown, 15 Coology 
but not new. The second paper, called “ Note on the si phlet, l 
Lower Merion and vicinity,” which is at the end of the pa Sur- 
is a criticism of Mr. Hall’s volume C, of the 2d Geologic e. 
1In the copy of Rogers’ final geological maps, before the writer, there Spread 
be a color indication of one of these detached Serpentine masses, Mner west 
Eagle tavern, in nearly a correct position, but of another exposure fi as the colo l 
is no indication, This, however, is not perfectly satisfactory annette serpentine 
in different copies, and the color for t ‘ 
