DOLERITE INTO HORNBLENDE-SCHIST. 145 



support to the extreme views held by some concerning the meta- 

 morphism of sedimentary rocks. 



Prof. Blake asked how it was that one part of the dyke was 

 changed while the other part was not. He objected to the view 

 that because the change might take place in a range of a few inches, 

 therefore great masses of rock could be changed in the same way. 



Mr. HuDLESTON remarked on the difference between the horn- 

 blende-schist of the dyke, consisting largely of hornblende and an 

 altered felspar, and the common hornblende-schist, which consists 

 chiefly of hornblende and quartz. 



Mr. KiLGouR called attention to the fact that by pressure a 

 similar fibrous structure is produced in cast-iron. 



The Author, in reply, pointed out that while the gneiss of the 

 country showed signs of great disturbance, the dyke maintained its 

 direction with a considerable amount of regularity. It seemed 

 evident then that the disturbances to which the gneiss had been 

 subjected must in the main have been produced before the intrusion 

 of the dyke. He had not argued that all hornblende-schists were 

 metamorphosed dolerites, but only that a particular hornblende-schist 

 been produced in this way. Why movement and metamorphism 

 had occurred at certain points and not at others he could not explain. 

 The typical schist of the dyke was composed almost entirely of 

 hornblende and a mineral or minerals occurring as colourless crys- 

 talline grains. Turbid felspar was rare, and, in the most perfect 

 schist, almost if not entirely absent. The colourless grains he 

 originally regarded as quartz, but he now felt considerable doubt as 

 to their precise character. In every respect, so far as his expe- 

 rience enabled him to judge, the schist appeared to resemble the 

 typical hornblende-schists of the so-called Archaean rocks. 



