FREE INSTITUTE OR, SCIENCE Š 
MINERALOGY OF THE NEWARK GROUP IN PENNSYLVANIA 
Careful consideration of these objections shows that they are not all of 
equal force. While it is no doubt true that zeolites do not form in modern 
sheets of lava a few feet thick, or near the upper surface of thicker sheets, neither 
have they been observed in corresponding positions in ancient lavas. The fine 
Specimens from the Watchung Mountain of New Jersey are all found near the 
base of the flow, and in the small extrusive sheet here being studied, the datolite 
and zeolites first appear at a depth of 350 feet. And these minerals are actually 
found in the deeper portions of the Vesuvian lavas, as Dana himself admits. 
In fact, the limitation of the secondary minerals to the lower portions is a strong 
argument against the theory of their formation by circulating surface waters, 
for this process should develop them uniformly throughout a lava mass. 
Fischer’s suggestion, that the fluorine and boron of secondary minerals 
might have been derived from original tourmaline or danburite, while it may 
be valid in the case of the formation of the zeolites in granites and gneisses, 
which he was considering, is of no application here, for tourmaline and danburite 
are not known as constituents of lavas or similar igneous rocks. The appearance 
of these elements in the secondary minerals can further not be explained by 
any ordinary weathering process, unless they are present in the unaltered igneous 
tock as original constituents. No studies having ever been carried out with a 
view of testing this point, with the exception of those of Fischer, in which the 
methods employed were not sufficiently delicate to really settle the matter, a 
thorough investigation of it was here undertaken. This will be described 
after considering the two remaining arguments for the w sathering theory. 
The third objection raised is a perfectly sound one, but it merely shows 
that the presence or absence of oxygen during the formation of the secondary 
minerals is not adequate to determine the source of the waters effecting the 
change. The final argument that degree of hydration might depend on the 
chemical nature of the solution as well as on the temperature at which the 
minerals form is also by no means a conclusive one. Too little is known con- 
cerning the conditions necessary for the development of any of the secondary 
minerals for this to have much value in deciding such a question. So the only 
possibility of throwing any light upon the matter rests with the study of the 
distribution of boron and fluorine. 
The elements boron and fluorine are among the most difficult to detect 
and determine known to the chemist. In fact, as far as fluorine is concerned, 
no absolutely certain method of detecting minute traces has as yet been devised. 
