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PROFESSOR F. I). ADAMS AND DR. J. T. NICOLSON 
merits comparatively low pressures, and materials, such as paper, wax, clay, &c.—much 
less resistant than the rocks themselves—were employed, so that while they have 
thrown much light upon the dynamics of mountain making, they have left the aspects 
of the subject referred to above, and especially dealt with in the present paper, 
untouched. In another series of interesting investigations, specimens of the rocks 
themselves have been submitted to the action of direct pressure or heat, the conditions 
being; otherwise those which obtain at the earth’s surface. Hodcikinson,'" for 
instance, showed that if thin ribs of stone, 7 feet long and 1 inch thick, properly 
supported at the extremities, are submitted to transverse strain they undergo a 
permanent deformation, no matter how small the strain to which they are subjected 
may be. He does not, however, state what stone he employed. Miallj in more 
elaborate experiments of a similar character, measured the amount of permanent 
deformation produced in thin slabs of gypsum and limestone. He found that a more 
marked deformation without rupture could lie obtained if these rocks were embedded 
in pitch before being submitted to the action of pressure. He could not, however, 
succeed in permanently deforming slates or sandstones to any noticeable extent. In 
the tests made at the Watertown Arsenal,J by employing greater pressure, a slight 
though permanent “ set ” was given not only to marble but to sandstone, and the 
same effect was produced by the simple application of heat without pressure. K,eyer§ 
has stated, as the result of experimental study, that while it is possible to slowly 
deform gypsum by the aid of low pressures continuously applied, the action is greatly 
accelerated if the material be kej)t, moist. 
A few other investigations, among which those of Gumbel and Kick are especially 
worthy of mention, bear more directly upon the question at issue. These have been 
designed with the object of reproducing, at least in some of their features, the condi¬ 
tions existing at great depths in the earth’s crust, and in this way bringing about 
such rock deformation as there results. Gumbel|| subjected little cylinders of 
orthoclase, quartz, Iceland spar and alabaster, enclosed in steel collars, and having an 
area of 1 centim. in cross section, and a height of between half a centim. and 1 
centim., to pressures varying from 22,000 to 25,000 atmospheres in a powerful testing 
machine. The cylinders of orthoclase and quartz crushed to an incoherent powder. 
The cylinder of calcite, on the other hand, retained its coherence. It became per- 
fectly opaque, and while still retaining its cleavage, is stated to have had a conchoidal 
fracture induced in it by the pressure. The cleavage faces showed their usual lustre, 
* ‘Athenaeum,’ 1853, p. 1165: “Report of the 23rd Meeting of the British Association for the 
Advancement of Science.” 
f “ Experiments on the Contortion of Mountain Limestone,” ‘ Geological Magazine,’ November, 1869 ; 
and a subsequent paper in the ‘ Popular Science Review.’ 
t Lof. cit. See also Mellard Reade’s ‘Origin of Mountain Ranges,’ pp. 16 and 24. 
§ ‘ Theoretische Geologie,’ p. 444. 
| “ Das Yerhalten der Schichtgesteine in gehogenen I agon,” ‘ Sitzungsber. d. konigl. Bayer. Akad. d. 
Wjss.’; Math. Phy. Classe, 1880, 4, 596-623. 
