File:The Quarterly journal of the Geological Society of London (13960477133).jpg

CRYSTALLINE

 ROCKS 
 OF 
 THE 
 MALVERN 
 HILLS. 
 503 
 

Dr.

 Irving 
 alluded 
 to 
 the 
 important 
 difference 
 presented 
 by 
 the 
 

phenomena

 of 
 the 
 shear-zones 
 and 
 those 
 of 
 the 
 masses 
 of 
 the 
 

gneisses.

 We 
 have 
 no 
 right 
 to 
 assume 
 that 
 these 
 rocks 
 are 
 meta- 
 

morphic

 in 
 their 
 origin. 
 The 
 question 
 of 
 the 
 replacement 
 of 
 bases 
 

is

 one 
 of 
 much 
 interest. 
 He 
 explained 
 how 
 potash 
 may 
 be 
 

replaced,

 and 
 gave 
 illustrations 
 : 
 there 
 would 
 be 
 variations 
 in 
 the 
 

results

 according 
 to 
 the 
 quantity 
 of 
 free 
 carbonic 
 acid 
 acting 
 on 
 the 
 

silicates.

The

 Author, 
 in 
 reply, 
 stated 
 that 
 he 
 had 
 not 
 raised 
 the 
 general 
 

question

 as 
 to 
 the 
 origin 
 of 
 the 
 crystalline 
 schists. 
 Mr. 
 Rutley 
 

recognized

 sedimentary 
 rocks 
 towards 
 the 
 south 
 end 
 of 
 the 
 chain. 
 

This

 appearance 
 was 
 simply 
 due 
 to 
 more 
 intense 
 shearing. 
 The 
 

rocks

 were 
 more 
 highly 
 quartzose, 
 the 
 result 
 of 
 more 
 intense 
 

metamorphism.

 The 
 crushed 
 rock 
 gradually 
 passes 
 into 
 the 
 recon- 
 

structed

 rock. 
 He 
 allowed 
 that 
 black 
 mica 
 may 
 be 
 derived 
 directly 
 

from

 hornblende, 
 but 
 that 
 was 
 not 
 the 
 case 
 in 
 the 
 Malvern 
 Hills. 
 

He

 dissented 
 from 
 the 
 notion 
 of 
 friction-breccia. 
 Mr. 
 Teall's 
 

point

 was 
 the 
 kernel 
 of 
 the 
 whole 
 question. 
 There 
 was 
 deformation 
 

at

 the 
 margins 
 of 
 the 
 zones, 
 but 
 not 
 in 
 the 
 centre, 
 because 
 the 
 rock 
 

had

 been 
 reconstructed 
 ; 
 eyes 
 of 
 felspar 
 are 
 often 
 seen 
 in 
 the 
 most 
 

highly

 fohated 
 rocks. 
 A 
 granular 
 structure 
 was 
 characteristic 
 of 
 

the

 reconstructed 
 bands. 
 There 
 was 
 no 
 distinction 
 between 
 smaller 
 

and

 larger 
 granite-veins. 
 He 
 referred 
 to 
 Prof. 
 Blake's 
 point 
 as 
 

to

 the 
 evidence 
 of 
 shearing 
 in 
 the 
 broken 
 hornblende 
 crystals. 
 

Most

 of 
 the 
 questions 
 raised 
 were 
 answered 
 in 
 the