24 TRANSACTIONS OF WAGNER 
MINERALOGY OF THE NEWARK GROUP IN PENNSYLVANIA 
With boron, however, there is a very delicate method of detection, the turmeric 
paper test, with which as little as 0.0001 milligram gives a distinct reaction. 
And for determination of small amounts in silicate rocks the writer has recently 
devised a method which is applicable, when carried out with special precautions, 
to quantities as small as. os milligram, or, working on т gram of rock, to .005%.'® 
For the present purpose it seemed unnecessary to attempt to obtain smaller 
quantities than this, for traces may be detected in practically every mineral 
substance, and could therefore have no significance here. 
In the intrusive sheet at Jacksonwald no secondary minerals were observed. 
In the extrusive sheet, however, they are abundant, not in fine large specimens 
like those from the First Watchung Mountain in New Jersey, for instance, 
yet quite typical and definite. Considering the Antietam Creek section, already 
described in detail, at the very top of the mass the gas cavities are empty, or 
at best, filled with red mud, but ten feet down they are solidly filled with calcite, 
together with more or less chloritic material. About 100 feet below the top 
prehnite begins to appear, chiefly in seams solidly replacing the decomposed 
trap, but occasionally showing small globular clusters of crystals where a cavity 
has been occupied. This prehnite replacement is limited to a belt about 50 
feet thick, although the same mineral occasionally accompanies the others in 
the cavities lower down. From 150 feet to 300 feet the calcite chlorite filling 
is again the rule, and here the cavities are sometimes nearly an inch in diameter. 
Then datolite begins to appear, filling both bubble cavities and cracks, but 
never in large amount nor in distinct crystals, being instead coarsely granular 
and intimately mixed with calcite. The occurrence of this datolite is limited 
to perhaps fifty feet of thickness of the trap, and no trace of the mineral has been 
noted in any other part of the sheet, nor at any other exposure. Below the 
datolite zone, as it may be called, gas cavities are much less prominent, and 
here the zeolites make their appearance along the joint planes. These com- 
prise stilbite, heulandite and chabazite, in small but typical crystals, the first 
usually alone, the last two usually associated; they are sparingly present 
through the remainder of the thickness of the sheet. At the very base there 
are a few elongated gas bubbles, mentioned above, and these are filled solidly 
or nearly so with white crystalline quartz. 
Twenty specimens from all parts of this sheet were examined, and all 
but two of them, both from the datolite zone, proved to be free from boron. 
Of these exceptions, one was situated within an inch of a large cavity containing 
