356 Canadian Record of Science. 



The third hypothesis, namely that the minerals in question 

 have been developed in the rock after its solidification, 

 perhaps by dynamic action, and indicate a first stage of 

 metamorphism but without complete re-crystallization, is 

 not nearly so startling as it might seem at the first glance. 

 We have examples of such a development in a number of 

 cases, and it may be that the growth of minerals in this 

 way is a much more common factor in development of 

 crystalline schists than is generally supposed. It is what 

 takes place in almost every case of pseudomorphism by 

 alteration. 



"All the rocks situated at considerable depths in the earth's 

 crust must be subject to great pressure resulting from the 

 weight of the superincumbent masses. Under these pressures, 

 liquids and gases may be made to penetrate between the 

 molecules of the solid crystals. The evidence that such 

 permeation of solid crystals by liquids and gases has 

 taken place is overwhelming. In the words of Van der 

 Waals, ' All bodies can mix with one another when the 

 pressure exceeds a certain value.' " ] That by the action of 

 such solutions secondary minerals may be developed is a 

 very reasonable supposition, and that they have been so 

 developed in the rocks at present under consideration seems 

 to be the explanation which best accords with facts observed. 



As a good example of the growth of one mineral in and 

 through another after the solidification of the rock of which 

 it is a component part, the development of wollastonite in 

 the plagiuclase, of a plagioclase-pyroxene rock from Brittany 

 described by Dr. Whitman Cross may be cited. 5 



Another example is the alteration of quartz into steatite 

 described by Dr. Weinschenk. 3 In this case the steatite was 

 found to grow in the crystals of quartz which were traversed 

 by very fine capillary cracks, thus forming a net work 



1 Chemical changes in rocks under Mechanieal Stresses " by Prof. J. W- Judd, 

 Journal of Chemical Society. May, 1890. (p. 410). 



2 " Studien uber bretonische Gesteine Tschermach's Min. u. Pet. Mittheil, 

 1880, iii.. 369." 



8 " Ueber die Umwandlung des Quarzes in Speckstein." Zeit. fur Kryst> 1888. 

 (p. 305). 



