Prof. J. W. Judd—Statical & Dynamical Metamorphism. 248 
IL.—On Srarican anp DynamicaL MrramMorPHisM. 
By Prof. Joun W. Jupp, F.R.S. 
T has long been recognized by geologists that rock-masses which 
have undergone movement, and have thereby been subjected to 
internal stresses, exhibit, as the consequence of the action upon them 
of such mechanical forces, unmistakeable evidences of having been 
greatly modified, alike in their mineralogical and in their 
structural characters. That the most complete and striking examples 
of such changes are to be found in the rock-masses which constitute 
mountain-chains—rock-masses which have actually been made to 
“flow,” and in so doing have been subjected to shearing movements 
of the most intense character—was clearly pointed out by Scrope, 
Darwin, Sharpe, Naumann, and Dana; all of whom referred the 
foliated structure exhibited by such rock-masses to this cause. 
The careful study, in recent years, of the actual processes involved 
in bringing about such changes, has rendered necessary the 
adoption of certain terms, to define the nature of the action in 
particular cases. In 1869, Lossen proposed to call the changes 
produced during rock-movements “ dislocation-metamorphism ”’ 
(dislocationsmetamorphismus) ;' while four year later Baltzer 
invented the term ‘‘ mechanical metamorphism” (mechanischer 
metamorphismus) ;* in 1884 Gosselet suggested the term “ friction- 
metamorphism” (métamorphisme par friction);* and in the 
following year Giimbel employed the name ‘“ compression-meta- 
morphism” (stauungsmetamorphose) ;* while in 1886 Bonney pro- 
posed to use the term ‘“ pressure-metamorphism.” ° 
Rosenbusch, in the same year, seeking to bring clearly into 
view the consideration that the special kind of metamorphism 
referred to is only produced when the mechanical forces effect 
movement, and thus do work, suggested the term Dynamical meta- 
morphism or dynamometamorphism ;° and this term, if not absolutely 
free from objections, is so convenient that it bids fair to be generally 
adopted. 
There is perhaps at the present time a tendency to exaggerate the 
results of this particular agency of dynamical metamorphism, and to 
overlook or minimize the importance of other contributory causes to 
the alteration of rock-masses. I desire in this note to call especial 
attention to the remarkable effects which result from the chemical 
and crystallizing processes which certainly go on at great depths, 
and under enormous pressures, even when the rock-masses do not yield 
to the pressures and thus become subjected to the movements which 
1 Zeitschr. d. d. geol. Gesellsch. Bd. xxi. pp. 282-340. 
2 Der Glarnisch (1873), p. 58. 
‘3 Ann, Soc. Géol. du Nord, xi. (1884), p. 188. 
4 Geol. von Bayern, i. p. 379. 
® Ann. Address Geol. Soc. Q J.G.S. vol. xlii. (1886), p. 62. 
5 Der Massige Gesteime, 2nd ed. 1886. 
