^12 DR. F. DIXEY ON THE [vol. Ixxviii, 



{2b) Field Relations of tlie Older and Younger Norites. 



Apart from several small isolated exposm^es on the mountains of 

 the peninsula, the younger norites crop out only along the fore- 



•shore on the south-western side. They occur as numerous 

 intrusions, many of them continuous under a thin roof of the 

 invaded rock. These intrusions are of all sizes up to a quarter of 

 a mile in length, and several of the larger ones form low capes, as 

 .for example, Grodrich Point (see p. 313). They do not show any 

 regular arrangement, except in one case, where four of them are 

 elongated along a line running east and west. They send out 

 numerous veins and tongues into the surrounding rocks. The 

 grey rounded masses of the coarse or ^^ounger norite are in most 



-cases readily distinguished from the well-jointed, dull-red blocks 



• of the normal.type. (See PI. XVI, fig. 2.) 



In certain places the junction of the older and younger norites 

 can be followed for as much as 100 yards, and is seen to consist of 



,a confused jumble, or intrusion-breccia, of the two types ; it 

 includes wide areas of the normal rock shattered and pierced by 

 numerous veins and tongues of the younger norite, and also 



•scattered blocks and fragments of the normal norite, some sharp 



.and angular and others deeply corroded. Even where the junction 

 is not so broad, it is often vague and difficult to follow because the 

 older rock has in some places been heated to a high temperature 



:and even re-fused. Away from the junction are a feiv isolated 

 masses of younger norite and of older norite, the former repre- 

 senting cupolas of the main intrusion, and the latter the remains 

 of pendants from the roof. Also, within the younger norite are 

 stoped blocks of the older norite, some of them moved only slightly 

 out of place, while others, carried a considerable distance, lie in 

 all directions. Moreover, some present clean fresh joint-faces to 

 the younger norite, and others show slight corrosion or deeply- 

 indented outlines. Yet others, while retaining their form, have 

 lost their original texture and composition ; finally, many are 

 completely shattered, and so permeated by the younger norite that 

 they are represented by a mixed rock showing only shreds of the 



■ original norite. (See Pi. XVII, fig. 1.) 



The invading magma nearly always cuts across the banding of 

 the older mass, and only in exceptional cases does it appear to 

 have induced any foliation. In these instances a few bands and 

 numerous streaks are associated with and arranged parallel to the 

 margins of the coarse intrusions, as if a gneiss, comparable in 

 structure and origin with (a) the 'streaky' phase of the Kennack 

 gneiss,^ and (,<3) the gneisses of Pum," had been formed by the 

 intermixture of plastic fragments of the older norite with the 

 viscous invading magma. This banding and streakiness is distin- 

 guished from the ordinary banding of the older norite by greater 



1 ' The Geology of the Lizard & Meneage ' Mem. Geol. Surv. 1912, p. 132. 



2 ' The Geology of the Small Isles of Inverness ' Mem. Geol. Surv. Scot. 

 .1908, p. 69. 



