TRANSACTIONS OF WAGNER 
MINERALOGY OF THE NEWARK GROUP IN PENNSYLVANIA 
26 
minerals. In the “Goat Hill” quarry, some 800 feet below the top of the sheet, 
on the New Jersey side of the river, datolite had been discovered in fine crystals 
by Mr. Harry W. Subers and the writer.about two ycars before, and one of the 
specimens then obtained was examined as had been done with the matrix of 
the Jacksonwald datolite. Here the trap was rather more compact, so that 
the datolite showed no sign of penetrating more than a few millimeters from the 
wall of the fissure in which it occurred. And the chemical examination failed 
to detect the slightest trace of boron in the samples of the rock used. 
Since, then, boron is absent from the igneous rock as a whole at both 
localities, and must have been given off while the magma was in process of 
solidification, it follows that the datolite, and presumably the various associated 
secondary minerals as well, can not have been formed by a simple weathering 
process. It is not, however, necessary to assume that they developed immediately 
after the intrusion or extrusion of the magmas. For while the upper and lower 
surfaces of the sheets may have cooled rather suddenly, the interior portions no 
doubt required many years to attain the temperature of their surroundings, 
thus allowing time for the appearance of the joint planes in which many of 
the secondary minerals have deposited, and possibly even permitting the ming- 
ling of the magmatic with surface waters, so that the later minerals may have 
been formed by a combination of the two processes. The abundance of calcite 
as the last mineral to form throughout many trap masses certainly suggests the 
action of surface waters containing abundant carbon dioxid. All that can be 
concluded from the present study, however, is that THE DATOLITE AND ASSOCIATED 
MINERALS OBSERVED IN TRAP SHEETS HAVE PROBABLY BEEN FORMED DURING 
SOME STAGE OF THE COOLING, AND NOT BY SUBSEQUENT WEATHERING. 
