374 The American Geologist. December, 1894 
I. Both arc unconformable with the gneiss upon which they rest. 
."). Both have in sum total the same chemical composition and are 
magnesian. 
(i. The altered crystalline condition of the white limestone is due to 
the intrusion of igneous masses audio regional metamorphism, while 
the blue limestone never contains such igneous injections. 
7. The presence of certain minerals, especially chondrodite, is not 
indicative of geological age. 
It is not the purpose to consider here the evidence of the 
age of the white or crystalline limestones of Sussex county, 
but merel} T to give the arguments advanced by the different 
sets of writers. It requires, however, evidence of a very posi- 
tive paleontological or stratigraphical character to overthrow 
the generally held opinion that these two very different lime- 
stones are of different age. 
The aye of crystalline limestones of Warren county. The 
largest area of crystalline limestones in New Jersey, next after 
that of Sussex county, embraces the Warren county outcrops 
along Jenny Jump mountain. The facts so far made out by 
a careful study of the latter, point to the conclusion that 
these limestones are distinct from the Cambrian blue magne- 
sian limestone which occurs in Kittatinny valley to the west, 
and that they are of pre-Cambrian age. 
Relations of the crystalline limestones to the gneisses. The 
isolated outcrops, A to E (see the foregoing map), of crystal- 
line limestone along the eastern edge of the mountain, are 
undoubtedly remnants of what was once a continuous band, 
and have been separated by erosion, the alluvium of Pequest 
meadows covering the former connections between the present 
outcrops. The limestone in these outcrops sometimes shows 
a faint banding, but very often is quite massive; and when 
banding is apparently present it is often so obscure that 
measurements of it are of doubtful value. Where present, the 
banding of the limestone is in general parallel with that of 
the gneiss. Granitoid gneiss bounds the limestone on the 
west wherever outcrops are found on the west side of the 
limestone. At two points, A antl D, banded granitoid gneiss 
is found on the east of the limestone, between it and Pe- 
quest meadows. Rock outcrops are wanting where the gneiss 
might be expected to be found, east of the other limestone 
outcrops of this belt. The banding of the limestone agrees 
