OF THE MALVERN HILLS. 



489 



The greatest vertical displacement indicated in the section is 

 connected with the fault which crosses Swinyard's Hill, and, as 

 drawn, it would appear to be about 8000 feet ; but it is very 

 probable that this amount of throw may be divided between this 

 and two other possible faults, one of which may occur in Phillips's 

 " Silurian pass " on the north of Swinyard's Hill, while the other 

 may be situated in " The Gullet " between Swinyard's Hill and 

 Midsummer Hill. This view derives some support from a statement 

 made by Dr. Holl to the effect that " the several passes which 

 divide the chain of the hills at intervals are probably, some of them 

 at least, determined by lines of fault, as the direction of the strike 

 of the rocks on opposite sides of these passes is, in some cases, 

 abruptly altered " *. 



No sharp demarcations occur between the Upper, Middle, and 

 Lower Archaean groups which I have here ventured to propose. 

 The ver3 r existence of any one of these groups depends upon the 

 predominance or paucity of schistose beds, upon characters dependent 

 upon coarseness of crystalline structure, thickness of bedding, and, 

 in fact, upon the general nature of the rocks which constitute each 

 group. 



Part II. 

 On the Hocles of the Malvern Hilh. 



In the first part of this paper the general structure of the 

 Malvern Range was considered ; but, at the time it was written, I 

 had not microscopically examined the rocks which were collected 

 during my stay in that district. 



The details of this microscopic examination mainly constitute 

 the second part of this paper ; and I may here state that the micro- 

 scopic evidence does not appear to me to disagree in any important 

 respect with the views advanced in the earlier communication, except 

 that truly eruptive rocks are more plentiful in the range than I had 

 at first imagined. The following details relate to specimens which 

 were selected as typical: — 



jSTo. 1. North Hill. Largest quarry on North face of hill. — Coarsely 

 crystalline rock, consisting of pinkish-brown or flesh-coloured 

 felspar, black hornblende, small scales of dark mica, and some 

 quartz. This rock shows very coarse and strongly marked folia- 

 tion, the hornblende and mica forming irregular and somewhat 

 lenticular streaks, which are often an inch or more in breadth 

 and are rudely parallel ; but the bands do not appear to be con- 

 tinuous, as a rule, for any great distance, and a band frequently 

 thins out altogether. This is the coarsest example of foliation I 

 have met with in the Malvern range. Under the microscope some 

 of the larger felspar-crystals are seen to be microcline, the twin- 

 lamellae crossing approximately at right angles and undergoing 

 maximum extinction when rotated 15°. Orthoclase twinned on the 



* Op. cit. p. 95. 



