File:The Quarterly journal of the Geological Society of London (13937406061).jpg

540

 MAJOR-GENERAL 
 C. 
 A. 
 M'MAHON 
 ON 
 THE 
 HORNBLENDE-SCHISTS 
 

dyke.

 Similarly 
 trie 
 two 
 granite 
 dykes 
 (G 
 1 
 , 
 G 
 2 
 ) 
 had 
 probably 
 an 
 

underground

 connexion 
 with 
 each 
 other 
 at 
 the 
 time 
 of 
 eruption. 
 

This,

 however, 
 is 
 a 
 mere 
 matter 
 of 
 inference, 
 as 
 owing 
 to 
 shingle 
 

and

 boulders 
 on 
 the 
 sea-shore 
 (not 
 to 
 mention 
 the 
 two 
 faults) 
 their 
 

onward

 course 
 cannot 
 be 
 traced, 
 nor 
 can 
 they 
 be 
 directly 
 connected 
 

with

 the 
 outcrop 
 of 
 the 
 " 
 granulitic 
 " 
 group 
 on 
 the 
 foreshore. 
 

Fig.

 12. 
 — 
 Diorite- 
 and 
 Granite-dykes 
 intrusive 
 in 
 Serpentine, 
 

Kennack

 Cove. 
 

D

 * 
 f 
 f 
 Q 
 s 
 G' 
 D. 
 

S,

 serpentine 
 ; 
 c, 
 c, 
 gabbro 
 ; 
 D 
 1 
 , 
 D 
 2 
 , 
 diorite 
 ; 
 G 
 1 
 , 
 G 
 2 
 , 
 granite 
 ; 
 /, 
 /, 
 faults. 
 

At

 G 
 2 
 , 
 D 
 2 
 we 
 see 
 the 
 diorite 
 and 
 granite 
 running 
 separate 
 courses 
 

through

 the 
 serpentine 
 ; 
 at 
 D 
 1 
 , 
 G 
 1 
 the 
 granite 
 has 
 followed 
 the 
 

diorite,

 and 
 for 
 a 
 short 
 distance 
 they 
 have 
 held 
 a 
 common 
 course. 
 

This

 circumstance, 
 taken 
 alone, 
 is 
 insufficient 
 to 
 justify 
 our 
 calling 
 

D

 1 
 , 
 G 
 1 
 an 
 intrusive 
 dyke 
 of 
 " 
 granulite." 
 

Mr.

 Somervail 
 states 
 that 
 at 
 the 
 west 
 end 
 of 
 Kennack 
 Cove 
 " 
 the 
 

dykes

 cutting 
 the 
 serpentine 
 are 
 seen 
 to 
 coalesce 
 with 
 the 
 ' 
 granu- 
 

litic

 ' 
 rocks 
 forming 
 the 
 foreshore." 
 My 
 last 
 visit 
 to 
 the 
 cove 
 was 
 

made

 at 
 a 
 time 
 particularly 
 favourable 
 for 
 observation. 
 It 
 was 
 at 
 

low

 water 
 at 
 spring- 
 tide, 
 and 
 recent 
 storms 
 had 
 swept 
 away 
 accumu- 
 

lations

 of 
 sand 
 and 
 shingle 
 to 
 such 
 an 
 extent 
 that 
 Mr. 
 Pox 
 saw 
 for 
 

the

 first 
 time 
 rocks 
 in 
 situ 
 that 
 on 
 every 
 previous 
 visit 
 had 
 been 
 buried 
 

six

 feet 
 deep 
 under 
 sand. 
 I 
 saw 
 that 
 the 
 porphyritic 
 diorite 
 had 
 

intruded

 profusely 
 into 
 ordinary 
 diorites 
 (presumably 
 the 
 dioritic 
 

rocks

 of 
 the 
 "granulitic" 
 group) 
 and 
 that 
 both 
 had 
 been 
 invaded 
 

and

 injected 
 by 
 intrusive 
 granite. 
 Granite-veins 
 may 
 be 
 seen 
 darting 
 

about

 in 
 all 
 directions, 
 crossing 
 and 
 recrossing 
 each 
 other 
 at 
 every 
 

angle,

 in 
 the 
 porphyritic 
 diorite 
 of 
 the 
 foreshore 
 ; 
 but 
 I 
 could 
 not 
 

directly

 connect 
 the 
 diorite 
 and 
 granite 
 of 
 the 
 foreshore 
 with 
 the 
 

diorite

 and 
 granite 
 of 
 the 
 serpentine-cliffs. 
 The 
 question 
 then 
 arises, 
 

Are

 they 
 portions 
 of 
 the 
 same 
 intrusions, 
 or 
 do 
 the 
 diorite 
 and 
 granite 
 

in

 the 
 cliffs 
 represent 
 intrusions 
 of 
 one 
 period, 
 and 
 the 
 diorite 
 and 
 

granite

 in 
 the 
 '• 
 granulitic 
 " 
 group 
 on 
 the 
 foreshore 
 those 
 of 
 another 
 

age

 ? 
 This 
 question 
 will 
 best 
 be 
 answered 
 after 
 the 
 consideration 
 of 
 

two

 other 
 sections. 
 

On

 the 
 occasion 
 of 
 my 
 last 
 visit 
 I 
 was 
 able, 
 thanks 
 to 
 Mr. 
 Fox's 
 

able

 guidance, 
 to 
 reach 
 a 
 very 
 interesting 
 spot, 
 only 
 exposed 
 for 
 a 
 

short

 time 
 at 
 spring-tide, 
 on 
 the 
 west 
 coast, 
 about 
 200 
 yards 
 east