94 The Paragenetic Relations of Minerals. 



The rocks in contact with granite are not in all cases dis- 

 turbed or penetrated by it. There can be no doubt that the 

 perfectly undisturbed strata surrounding the granitic mass at 

 Aue, near Schneeberg, were formerly continuous. Their 

 place, however, is now occupied by granite. The fact, that 

 at the surfaces of contact of these strata with the granite, 

 there is a great preponderance of quartz crystals, those seated 

 upon the slate being remarkably large, and projecting into 

 the granite, as from the saalbands of a lodes, is a sufficient 

 proof that this change consisted, not in any actual fusion of 

 the rock, but merely in a softening which permitted a new che- 

 mical adjustment of the elements. It is not at all improbable 

 that the primitive mass from which this group of rocks was 

 formed was still liquid at some depth, and that when, from 

 some cause, the gneiss was again softened or rendered pasty, 

 it assumed, upon after solidification, the form, not of gneiss, 

 but of granite ; for, during this second solidification, at a 

 depth below the surface, the mass would have been beyond 

 the influence of those disturbing causes which have already 

 been alluded to as probably inducing the stratification of 

 gneiss. 



All the members of this group probably resemble each 

 other as much in regard to the temperatures at which they 

 were formed as they do in date. From the analogy, in all 

 essential points, between granite and granulite, granite and 

 gneiss, granite and mica-slate, there is no ground for assum- 

 ing that one was of igneous and another of aqueous origin. 



The differences presented by the individual rocks of this 

 group is but a very slight obstacle to the opinion that they 

 have originated from the same primitive mass, especially when 

 it is remembered how greatly the petrographic character of 

 granite or gneiss varies, even in the same mass ; that the oc- 

 currence of certain accessory constituents is confined to par- 

 ticular spots ; and that they all pass into each other accord- 

 ing to the presence or absence of one or other of these con- 

 stituents. 



The views entertained with regard to the sedimentary 

 members of the group of crystalline rocks are very different, 

 and even opposite. That which regards them as altered me- 



