364 
PROFESSOR F. D. ADAMS AND DR. J. T. NICOLSON 
matter concerning which there has been much discussion and a wide divergence ot 
opinion. Some authorities—among whom Heim,* whose work in Alpine geology 
must command the admiration of all, may be mentioned—have held that while, in the 
upper portions of the earth’s crust, rocks, when submitted to pressure, will break, 
giving rise to faults and overthrusts, the same rocks in the deeper portions of the 
earth’s crust are unable to break up in this way, owing to the great weight of the 
superincumbent strata. The lines of fracture become smaller and greatly increase in 
number, the various minerals constituting the rock thus breaking down into grains, 
which, however, move around and past one another, the adjacent grains always 
remaining within the sphere of cohesion. The structure becomes cataclastic ; the rock 
mass, acting as plastic bodies do, and flowing in the direction of least resistance, 
maintains its coherence while altering its shape. Heim believes that there is a 
further stage in the process which he thus describes :— 
“ Wird die umformende Kraft endlich so gross dass sie anstatt an ein, paar tausend 
Stellen die Festigke.it durch Bruch aufheben zu konnen, dieselbe in jedem einzelnen 
Punkte iiberwindet, so wird das Spaltennetz unendlich fein und das Gesteinskorn zur 
Kleinheit eines Molekiiles reducirt, d. h. die mechanische Bewegungseinheit ist nicht 
mehr ein Gesteinsbrocken sondern unendlich klein so dass die Bewegung eine 
continuirliche Umformung ohne Bruch wird.” 
Now, according to Spring,! the property known as regelation is really due to a 
power which fragments of bodies have of uniting if brought within the range of the 
molecular forces, a property which, although possessed in a marked manner by ice, is 
also, as he has experimentally demonstrated, exhibited by many other bodies, and 
would probably be displayed by all if the required conditions could he attained. The 
“flow of rocks” would therefore, according to this view, be a manifestation of 
regelation on an enormous scale. 
Other writers on this subject have maintained that rocks are absolutely destitute of 
plasticity in any proper sense of the term. Thus Mallet| based his theory on the 
supposition that in the earth’s crust rocks under pressure are shattered. Pfaff§ has 
held that in the depths of the earth great pressure alone will tend rather to prevent 
molecular movement and thus keep the rocks rigid. Those holding such views 
attribute the deformation of rocks either to crushing with subsequent recementation 
of the fragments by mineral matter deposited from percolating waters as the 
movements proceed or after they are completed,|| or to a continuous jirocess of 
* ‘ Der Mechanismus der Gebirgsbildung,’ p. 31 ; see also Van Hise, C. R., “Metamorphism of Rocks 
and Rock Flowage,” ‘ Bull. Geol. Soc. of America,’ vol. 9, 1898. 
t “ Recherches sur la propriete que possedent les corps de se souder sous Taction de la pression.” 
‘Revue Universelle des Mines,’ 1880. 
| ‘ Philosophical Transactions,’vol. 163, 1874. 
§ ‘Der Mechanismus der Gebirgsbildung,’ pp. 19-21. 
|| Stapff, “Zur Mechanik der Schichtenfaltungen,” ‘Neues Jahrbuch fur Mineralogie,’ 1879, p. 792; 
Reyer, ‘ Theoretische Geologie,’p. 443. 
