246 The American Geologist. April, i89i 
tion of crystalline structure down to a finely granular one, and 
even to what may be termed the subcrystalline condition, when it 
often partakes of the color and texture of the blue limestone out 
of which all these varieties have originated. " 
On pages 73 and 7G of this final report Prof. Rogers describes 
very minutely, two localities in which a change from the unaltered 
blue limestone to the highly crystalline limestone takes place 
within a distance of fift} T feet. 
In one of these localities at Lion pond, now Roseville pond, 
there is a regular gradation from the S. E. First gneiss, second 
sandstone Formation I, third, blue limestone Formation II, pass- 
ing into the sandstones, and finally, the white crj-stalline lime- 
stones in contact with a dike of feldspathic sienite to which he 
ascribes the cause of alteration. 
Another very important fact recorded by Prof. Rogers (in this 
report, p. 74,) is the presence of the mineral chondrodite in these 
altered limestones. He notes that the abundance and perfection 
of the crystallization of this mineral bears a direct ratio to the 
crystallization of the limestone and this to the proximity to an 
igneous rock. 
I have thus briefly stated the outline of this report by Prof. 
Rogers. It will be seen that he committed himself unhesitatingly 
to the idea, first, that granites or sienites were eruptive ; second, 
that these eruptive rocks caused the metamorphism of the blue 
limestones, in places, to the highly crystalline white limestones 
of this region. 
It does not vitiate the truth of his observations in this case, 
that he went still farther and assumed the eruptive nature, not only 
of the granites and greenstones, but of the magnetite iron and of 
the zinc ores of the highlands of Sussex county especially. 
On this basis however he would have had hard work to account 
for the presence of sphalerite beds in the same limestone belt but 
nearer the Delaware river. 
Even in this brief sketch it is very evident that, however bril- 
liant the conception of this idea of the metamorphism of the blue 
limestone may have been, it was more in the line of geological spec- 
ulation, and he fell far short of proving his position, though in 
comparison with the recorded observations of Yanuxem and Keat- 
ing his demonstration is perfect. A careful reading of his whole 
report on this subject does little more than to multiply instances 
