690 Prof. J. Joly on the Closure of Small 



From March 27th to March 28th, 1914, 20 tons were applied; 

 and from March 28th to Sept. 19th, i. e. 175 days, 30 tons. 

 The results were a small collection of del>ris manifestly 

 spalled off the walls of the cavity, in the case of the Solenhofen 

 rock. The covering surface was cracked and broken out- 

 wards round the edges of the circular area of no pressure. 

 In the case of the obsidian there was a small amount of 

 debris in the cavity, and the flat surface was very faintly 

 bulged outwards over the central circular area. 



This experiment, taken along with (II. ), clearly shows that 

 in 30 tons on the plunger, that is 38*70 tons or 88,717 lb. per 

 square inch ( = 6100 kilos per sq. cm.), we have a pressure 

 which is certainly sufficient to close cavities in granite, 

 basalt, obsidian, or limestone. 



Here the experiments had to come to an end, the prepared 

 material being exhausted. It had been intended to apply 

 to Dr. Krantz for additional spheres^ but, of course, war 

 conditions rendered this impossible Modifications of the 

 crushing apparatus permitting of prolonged application of 

 temperatures up to about 500° C. were designed, but there 

 was no possibility of having these carried out. 



So far as they go, the experiments show that for the four 

 different varieties of rocks tested the pressure of 88,700 lb. per 

 square inch, i. e. 6100 kilos per square cm., must even in the 

 cold close all cavities in the rock, and at the probable tempe- 

 ratures attending such pressures (between 800° and 900° C.) 

 must be considerably in excess of the critical pressure. And 

 further, that the signs of yielding in the cases of granite and 

 basalt at the pressure of 59,100 lb. per square inch, i. e. 

 4067 kilos per sq. cm., are sufficient to justify the assumption 

 that at the probable corresponding earth temperature (450° 0.) 

 this pressure must be near the critical pressure for these 

 materials. 



Microscopic examination of the granite and basalt shows 

 that these rocks are quite typical varieties. The granite has 

 two micas, a brown mica partially chloritised (and containing 

 abundant haloes) and a limpid mica (muscovite). Most of 

 the felspar is plagioclase ; a part is orthochise. All the 

 felspar is fresh and limpid. There is abundant quartz 

 showing the usual strings -of fine bubbles or cavities. The 

 structure is typically granitic. The basalt has fine olivines, 

 augite, and basic felspar. It is very fine-grained. The 

 phenocrysts are augite mainly. No glass was detected. The 

 obsidian was not examined microscopically. It was obviously 

 a. very homogeneous glass. A few very minute bubbles or 



