White LimestQiies of Sussex County, X. ■/. — Kason. 1(57 
range of magnesia is very great, but it is never absent from 
either variety as shown by the analyses. In considering the 
chemical composition of these rocks as a whole, the composi- 
tion and distribution of the minerals contained in the white 
limestone must also be taken into account. These are con- 
fined to the vicinity of eruptive rocks, especially the granites 
and scapolite diorites: and it will be there found that the 
carbonate rock which contains them is now low in magnesia. 
It will also be observed that the principal minerals are those 
high in magnesia, such as phlogopite, biotite, pyroxene, horn- 
blende and especially chondrodite. which is the most abundant 
of all and contains over 50 per cent, of it. Considering, then, 
the foregoing facts, it is impossible to escape the conclusions 
that the magnesia in the minerals has been derived wholly 
from the rock in which they are now found, and that the con- 
taining limestone was formerly a dolomite and has become 
de-dolomitized by the metamorphic action of the intruded 
granites and other eruptives. Were the magnesia now locked 
up in these minerals re-distributed in the form of a carbonate 
through the containing limestone, the result would be a dolo- 
mite in no way distinguishable from either the white or blue 
dolomite. 
6. Present condition of the white limestones due to igneous 
rocks. The white limestones and the blue as well are not 
isolated, the one from the other, but they lie in the same val- 
ley, shifting from side to side with the appearance of granite 
or other intrusive rocks. Moreover, the white limestones are 
never found outside of a greatly disturbed belt, and never 
far distant from igneous masses. This point has been touched 
upon so many times that it is hardly necessary to repeat it. 
but the fact is so patent to a held observer that it cannot ln- 
emphasized too strongly. The crushing, heat, and pressure, 
resulting from this great complex of intrusions, were amply 
sufficient to completely metamorphose much more refractory 
sediments than these. 
7. Chondrodite not indicative of geological age. The min- 
erals associated with the white limestones have long been 
used as an argument in support of its Archaean age. So many 
of them, however, have been shown in various localities to be 
merely the result of metamorphic action of intruded igneous 
