264 J. Parldmon — The Making of Quartz Schist. 



a high elastic limit and considerable ductility. The marble, which 

 alone was subjected to pressure, was shorter than its casing, and 

 was squeezed by means of plugs passing into the ends of the, jacket; 

 pressure being continued until the bulging of the latter was carried 

 almost to the point of rupture. The rock was squeezed under three 

 sets of conditions — in the first at normal temperature and dryness ; 

 in the second heated to 300°-4:00° C. ; and in the third permeated by 

 water vapour at a pressure of 460 lbs. per square inch, the heating 

 being the same as in the second series. The following results 

 appear significant. 



1. The crushing load of the deformed marble of the first series 

 was considerably less than that of the natural rock ; due, it is 

 thought, to the production of ' cataclastic structure ' along certain 

 lines ; in the second series the crushing loads were nearly equal, 

 and in the third series that of the deformed rock was at least equal ^ 

 to that of the natural. Messrs. Adams and Nicolson remark that in 

 these experiments the presence of water was not observed to exert 

 any influence. 



The absence of cataclastic structure in series two and three and 

 the high crushing load of the deformed rock indicate that the 

 constituent gi'ains of the marble have suffered no loss of elasticity, 

 but that the conditions were such as to allow different molecular 

 groupings as the pressure increased. 



2. The experimenters conclude that under the second and third 

 sets of conditions the marble " has not been crushed in the ordinary 

 sense of the terra," but that deformation has been principally produced 

 by slipping on the gliding planes of the component crystals. 



3. The shape and character of the grains thus produced closely 

 resemble those of a schist. 



In accord with these results is the conclusion reached by Messrs. 

 Ewing and Eosenhain- in describing the deformation of certain 

 metals, that "each crystalline grain changes its shape through slips 

 occurring within itself, and its position through slips occurring in 

 other grains " ; and they point out elsewhere ^ that, if the adaptability 

 of the grains to accommodate themselves to the increasing pressure by 

 this means is insufficient they will be " driven into and through one 

 another"; a result readily conceivable in the case of such a material 

 as lead, but which, in the widely different substances usually con- 

 sidered by the geologist, seems to require something more than 

 mere pressure. 



The ' Upper Slate Member ' of the Penokee Iron-bearing rocks 

 (Huronian) described by Irving and Van Hise* is a case where the 

 work of pressure appears to have been reduced to a minimum. 

 Here we have the production of a new rock from a greywacke, 

 a quartz or mica schist in which no trace of a clastic origin remains. 



* Sufficient experiments were not made to determine this point. 

 - Proc. Eoy. Soc, 1899, vol. Ixv, p. 90. 



^ In an experiment on " the effect of very severe strain on lead" : Phil. Trans., 

 1901, vol. 195 a, p. 285. 



* U.S. Geol. Surv. Monographs, xix, 1892, p. 296. 



