and Rock Densities at High Temperatures. 33 



good agreement with this is the coefficient of 25*5 X 10" 6 for 

 the contraction of the expanded rock from 1000° to 0°. 



Comparing the volume of the crystalline rock with that of 

 the glass, and taking the volume of the glass as the basis of 

 comparison, we find that the difference of 7*1 per cent at 0° 

 has increased to a value between 9*1 per cent as a minimum 

 and 10'9 per cent as a maximum, the true value being much 

 nearer to 10 - 9 than 9*1. 



9. Shale and Sandstone. 



One series of measurements was made on a specimen of the 

 shale which underlies the Palisade diabase at Granton. The 

 block weighed 68*35 grams after drying four hours at 106°. 

 Measurements were made with tin as the immersion liquid. 

 The volume curve showed the characteristic break at 575° due 

 to the inversion of the quartz which was present in the rock 

 (see curves for granite, figs. 7 and 8). At 675° considerable 

 quantities of gas began to come off, interfering with the vol- 

 ume measurements, and the gas evolution continued up to 

 1090°. The rock was held between 1090° and 1113° for 80 

 minutes ; at the end of this time its volume had increased to 

 563, an expansion of 46 per cent. This was found to be due 

 to the formation of a spongy mass through the entrapping 

 of innumerable bubbles within the partly fused rock. Subse- 

 quent microscopic examination of the original shale showed the 

 presence of datolite in the interstitial spaces : this accounts in 

 large part for the behavior of the shale on heating. Datolite 

 was also found in the arkose sandstone. Its presence renders 

 these rocks unsuitable for volume measurements to a high tem- 

 perature. 



Measurements were also attempted on natural microcline, 

 and a satisfactory curve was obtained as far as 600°. At 

 higher temperatures the gas evolution again proved our un- 

 doing, causing shattering of the mineral in the solid state and 

 yielding a bubbly glass at the melting point, the liquid being 

 too viscous to allow the bubbles to escape. 



10. Geological Applications. 



Quartz and granite. — The volume change in quartz between 

 0° and 500° is 2-8 per cent, and between 500° and 575° it is 

 2"4 per cent, of the volume at 0°. In other words, the increase 

 during the last 75° before the transition point from low to 

 high temperature quartz is nearly as great as the increase dur- 

 ing the preceding 500°. A volume change as rapid as this 

 must be of considerable significance in the crystallization of 

 the siliceous rocks. As Fenner has pointed out in his recent 



Am. Jour. Sci. — Fourth Series, Vol. XXXVII, No. 217.— January, 1914. 

 3 



