76 PBOCEEDINGS OP THE GEOLOGICAL SOCIETY. 



is succeeded by thinner-bedded gneiss as far as the fosse, and for a 

 short distance beyond it *. 



Between the fosse and the summit of the hill there is a large 

 irregular mass of erupted trap, which sends a branch southward into 

 the hollow between the two spurs. This trap rock is precisely 

 similar to that of the summit of the Eagged-stone Hill, ancl, as will 

 be seen hereafter, to all the other traps associated with the crystal- 

 line rocks. In the immediate vicinity of the trap the rocks are 

 chiefly fine-grained gneiss, partly micaceous and partly hornblendic. 

 On the north side of the summit, the hill is composed entirely of 

 thin-bedded gneiss and mica-schist, containing dark-brown mica, 

 and ranging from north-west and south-east to west-north-west 

 and east-south-east nearly, and either vertical or inclined at a high 

 angle t- 



In the eastern ridge the rocks are not well exposed. A quarry at 

 its southern extremity shows some grey mica-schist, and at its 

 northern end are gneissie rocks having a nearly north and south 

 strike. Some coarsely crystallized hornblende- and felspar-rock 

 protrudes through the turf near the central parts of the hill, and 

 the fragments lying about show the rocks generally to be of the 

 same gneissie character as those of the western ridge. 



4. Sivinyards Hill. — In the narrow hill which succeeds to the 

 last, called Swinyards HiU, the strike of the beds is for the most 

 part east and west ; but in the quarry at the southern extremity, 

 near Fair Oaks, there is some contortion of the beds, with a general 

 south-easterly dip ; and towards the northern extremity of the hill, 

 the strike of the beds becomes north-west and south-east. The 

 hill is flanked on either side by the higher beds of the May Hill 

 Sandstone, those on its eastern side occupying part of Castle Moreton 

 Common, and separating the crystalline rocks from the Trias, which 

 has hitherto been in close proximity to them +. 



The following section taken along the crest of the hill, com- 

 mencing at its southern extremity, although slightly generalized, 

 and not perhaps entirely correct in all its details, inasmuch as there 

 may be minor bands which are not exposed, nevertheless gives a 

 sufficiently accurate notion of the structure of the hUl §. 



feet. 

 1. Micaceous schist and fine-grained gneissie rocks, with a 



few subordinate bands of hornblende-schist 665 



* In noticing the laminated structui'e of some of these rocks. Professor Philh'ps 

 observes, " Sometimes tlie felspar and mica, or felspar, hornblende, and mica, are 

 so arranged as to produce vertical lamination. It is difficult in that case to 

 refuse the rock the title of gneiss " (pp. cit. p. 28). 



t See also Professor Phillips, op. cit. p. 28, in which the laminated structure 

 of these rocks is especially noticed. 



X By some error in the colouring of the Ordnance Map, the May HiU Rock 

 on the east of this hill is represented as Hollybush sandstone. In the skeleton- 

 maps of Professor Philhps [pp. cit. pp. 60, 84) it is correctly entered as May 

 Hill Sandstone (Upper Caradoc). 



§ Owing to the inequality of the ground, and the difficulty of drawing clear 

 lines of demarcation between the beds, the thicknesses given can only be regarded 

 as approximative. 



