and Rock Densities at High Temperatures. 25 



periraents at atmospheric pressure, but it would become zero 

 only at depths where the minerals would flow or redissolve and 

 fill all pore spaces. 



8. Diabase. 



The diabase used was from the quarry of the Fairview 

 Stone Crushing Company, near Gran ton, N. J. The diabase 

 exposed at this locality appears to be an offshoot of the great 

 Palisades sheet which outcrops along the Hudson River and 

 southwestward through New jersey. The particular specimen 

 in question, in the form of a 100 lb. block, was from the lower 

 contact of the diabase against the underlying Newark (Triassic) 

 shale and sandstone. 



Prof. J. Volney Lewis, who collected this material for us, 

 has described the rock in his report on the " Petrography of 

 the Newark Igneous Rocks of New Jersey."* At the locality 

 in question there was, until quarrying operations followed it 

 back into the underlying strata, an excellent example of a type 

 of inclusion frequently occurring in the Palisade diabase, 

 namely, slabs of the underlying shale or arkosic sandstone which 

 have been " floated " up into the igneous rock. These occur 

 in various parts of the sheet and stand at various angles 

 between horizontal and vertical.f 



It was therefore of interest to compare the volume of the 

 molten diabase with that of the solid arkose and shale at the 

 same temperature. 



Our experience with granite had already convinced us that 

 the expansion of a complex rock can not be accurately deter- 

 mined by direct measurement above a few hundred degrees, 

 because of the shattering due to the unequal expansion of the 

 different minerals. Furthermore, a trial series on a pyroxenite 

 showed that when the rock was heated up directly through its 

 fusion range, its volume change in liquefying was concealed by 

 the escape of a large amount of gas, which swelled the half- 

 melted pasty rock into a sponge so voluminous as to cause the 

 tin to overflow and thus spoil the series of measurements. 



We therefore made a glass of the rock by- fusion in«the open 

 air, thus permitting the escape of all bubbles, followed by 

 rapid cooling. The rock was fused in a cylindrical crucible 

 made of platinum foil - 05 mm thick; the foil was then stripped 

 from the glass when cold, leaving a block of the proper dimen- 

 sions. 



Each melt was held for a few minutes between 1300° and 

 1350° until all bubbles had escaped from the liquid. When 



* Geol. Surv. New Jersey, Ann. Rept. 1907, 97-168. See in particular, 

 plate XVI ; analyses V and XII, p. 121, and p. 127. 

 t Ibid., p. 135 and plate XXVII, fig. 2. 



