498 PROF. T. G. BONNET AND MA JOE-GEN. C. A. M'^JIAHON 



(6) That earth-movements have produced marked effects only at 

 the extreme north and the extreme south of the district ; these, in 

 the former, modify the rocks for a very limited distance from the 

 boundary faults. In the latter the results appear to be on a some- 

 what greater scale. To this cause we attribute the " slatiness " 

 characteristic of the so-called Micaceous Group. Probably the latter 

 rocks are separated from the coarse gneisses of the outlying islands 

 on the south coast by a fault of low hade towards the north, which 

 emerges near the base of the present cliffs. 



EXPLANATION OF PLATE XYI. 



Fragment of banded set-pentine (natural size) picked up at foot of diffs, Porth- 

 alla (p. 474). is a joint-face, from which cracks, now closed by light- 

 coloured steatite, run for some little distance into the mass. Below AB 

 is a similar structure which, together with the change in the character of 

 the serpentine, suggests the possibility of one variety being intrusive into 

 the other. It may, however, only be another old joint-plane now closed. 

 This structure is described in Quart. Journ. Geol, Soc. vol. xxxix. (1883) 

 p. 22. 



DisctrssTON. 



Mr. Teall said that he had no general theory as to the relations 

 of the Lizard rocks. The views of the Authors as to the origin of 

 the Granulitic Group were not opposed to those which he had ex- 

 pressed. Tliey went farther than he had done, and maintained that 

 the deformation was connected with the intrusion of the granite. 

 There was a difference between him and the Authors as to the 

 origin of the foliation in the gabbro ; but, as he had no new facts 

 to offer, he did not wish to reiterate or to retract his opinions on this 

 subject. 



The Bev. Edwin Hill had accompanied the Authors with pre- 

 conceived opinions that the Granulitic Group had something sedi- 

 mentary in it, and that the gabbro-banding had something to do 

 with cooling at the surfaces of the intrusive masses. But he had 

 been constrained to admit that the granulitic banding was due to 

 injection by one rock into another. This other possibly had a pre- 

 existing structure sufficient to determine the lines of injection ; but 

 it was not necessary to assume such. So with the banded gabbro, 

 the evidence for the Authors' conclusions seemed complete. Though 

 " convinced against his will," he did not remain " of the same 

 opinion still." 



Prof. Hull wished to call attention to the remarkable resemblance 

 between some of the geological phenomena described so lucidly by 

 the Authors of the paper and those of some parts of Ireland, parti- 

 cularly in the Connemara and Donegal highlands. This resem- 

 blance might be recognized in the cases of inosculation of granitoid 

 with hornblendic masses, and the presence of serpentine breaking 

 through in d^'ke-like manner the older rocks. In Connemara there 

 were two varieties of serpentine : first, the dense, heavy, dark green 

 variety, which was, in all probability, a transformed augitic or 



