TKANSACTIONS OF SECTION C. 719 



MONDAY, AUGUST 8. 



The President's Address (see p. 695) was delivered, and the following Papers 

 were read : — 



1. On the Relation of the Bunter Pebbles of the English Midlands to those 

 in the Old Red Sandstone Conglomerates of Scotland. By Professor 

 T. G. Bonnet, D.Sc, F.R.S. 



The author had recently examined the conglomerates near Brodick (Arran), 

 at Rothesay, and in the neighbourhood of Callander. He had already expressed 

 the opinion that the quartzites in the Midland Bunter Pebble Beds were identical 

 with those abundant in Arran, and was convinced this was the case. The felstone 

 pebbles found in the Midlands were, he was now satisfied, similar to the Scotch 

 felstones, which occur both in situ and as pebbles in the Old Red Sandstone con- 

 glomerates, and in more than one locality in the latter he had found a peculiar 

 quartz-felspar grit (like Torridon Sandstone), which occurs also in the Midland 

 Pebble Beds. 



2. On the Relations of the Rocks of the Lizard District. 

 By Alex. Somervail. 



These rocks include the hornblende-schist, serpentine, gabbro, granite, &c., 

 which the author regards as all belonging to the same period of geological time, 

 and to have segregated or separated out from each other during the cooling of a 

 homogeneous magma. 



There seems absolute evidence in the field to show that the serpentine is a non- 

 intrusive rock, that it was the first portion of the magma to cool, and is broken 

 through by all the other rocks, but that it is intrusive into none. 



The relations between the serpentine and the diorite and portions of the granu- 

 litic rocks are those of segregation, and not of intrusion, as many sections show 

 these rocks associated together in great alternating bands with a concentric-like 

 structure with complete transition varieties, but with no signs of intrusion on the 

 part of either. These concentric-like structures, which are certainly original— due 

 to cooling — have been subsequently displaced and broken up, so that the now 

 isolated portions are mistaken for intrusive tongues of serpentine or included frag- 

 ments of hornblende. When followed out they resolve themselves into what were 

 once connected masses. 



While the main masses of these rocks have separated out from each other, and 

 cooled in the order of increasing acidity, there also seems absolute proof in the field 

 that the intrusive dykes in the serpentine, consisting of diorite, granite, complexes 

 of these and also of gabbro, are but portions of the uncooled magma of the main 

 masses which were able to penetrate the serpentine. 



That the main masses and the dykes are of one and the same age is evident, 

 not only from their mineral composition and lithological aspect, but also from the 

 fact that all these rocks are inter-related — for example, the gabbro and diorite 

 dykes coalesce, and dykes of the former have margins of the latter. The diorite 

 contains inclusions of gabbro, and in some instances inclusions of the latter contain 

 others of the former. The granulitic rocks, diorite, and gabbro occur as a regular 

 interbanded series, and there are also schists of these complexes. 



The facts seem to warrant the following conclusions : — 



1. That all these rocks belong to one geological epoch ; that their relations are 

 principally those of segregation or separation, and in a lesser degree of contempo- 

 raneous intrusion on the part of the less basic and more acid portions of the 

 magma. 



2. That the olivine portion of the magma now forming the serpentine was the 

 first to cool, followed by the others in the order of their increasing acidity. 



'.J. That the serpentine is a non-intrusive rock, and one into which all the other 

 types of rock have been intruded, the granite intrusions being the latest. 



