THE FLOW OF SOLIDS,* 
OR THE BEHAVIOR OF SOLIDS UNDER HIGH PRESSURE. 
By WILLIAM HALLOCK. 
Among the many physical questions that are of vital interest to the 
student of structural geology the one which may well contend for a 
position in the front rank is, What is the effect of pressure, with or 
without a rise of temperature, upon the rocks and rock-making magmas 
which form the outer shells of our earth? As avery important subdi- 
vision of this general question we have this: What is the effect of pres- 
sures upon so-called solids without any rise in temperature above a point 
far removed from the ordinary melting point? In other words, can we 
liquefy solids by pressure alone? As corollaries we have any pecu- 
jiarities at the instant of liquefaction and possible chemical reaction 
during this state of enforced liquidity. 
These questions have long formed the subject of theoretical discus- 
sion, but in spite of the fundamental importance of their satisfactory 
and final settlement they have seldom been investigated experimen- 
tally, doubtless owing to the difficulty of obtaining, measuring, and 
managing sufficiently high. pressures. 
Walther Spring may perhaps be rightfully called the pioneer in this 
work, having within the last few years published the results of much 
experimental work upon this question. His memoirst would seem to 
prove without doubt and finally, that pressures under 7,000 atmos- 
pheres will liquefy the large majorityt of solids, and it is only a ques- 
*From Bulletin No. 55 of the U. S. Geological Survey. 
+t Bull de Vv Acad. de Belg., 1880, 2d ser., vol. XLIx, and 1885, 3d ser., vol. Ix; and 
Bull, de la Soc. Chim. de Paris, 1883, vol. XXxX1rx, and 1886, vol. XLVI. 
t Bull. de V Acad, de Belg., 1880, 2d ser., vol. XLIx. 
237 
