Reports and Proceedings — Geological Society of London. 135 



12 feet thick; succeeded by {I) White Chalk with Ostrea limata, 

 about 20 feet ; {c) White Chalk without 0. lunata, about 8 feet ; 

 {d) White Chalk with 0. lunata, about 10 feet; and (e) Grey Chalk, 

 about 25 feet. There is no evidence as to the relative positions of 

 these two main divisions. The author seeks to justify his adoption 

 of Terehratidina gracilis and T. Gisei as the zone fossils of the 

 Trimmingham Chalk, in opposition to the proposal to adopt Ostrea 

 lunata as the zone fossil. Other .important species are Pentacrinus 

 Agassizi, P. Bronni, and Echinoconus Orlignyanus. The author still 

 adheres to his view that these masses of Chalk can only be in situ and 

 must have once formed part of a large continuous mass, and that the 

 bulk of this mass must have lain to seawards of the present coast-line. 



11.— Fehruarij 5th, 1908.— Sir Archibald Geikie, K.C.B., D.C.L,, 

 ScD., Sec. E..S., President, in the Chair. 



The following communications were read : — 



1. "On Antigorite and the Val Antigorio, with Notes on other 

 Serpentines containing that Mineral." By Professor T. G. Bonney, 

 Sc.D., LL.D., F.R.S., F.G.S. 



It is by no means certain, as the author ascertained after his joint 

 paper -with Miss Raisin, published in 1905, that the first described 

 specimen of antigorite was really found in the Val Antigorio. So last 

 summer he visited that valley, in company with the Rev. E. Hill, 

 and after an examination, of which he gives an account, came to the 

 conclusion that the rock most probably does not occur there m situ, 

 though it is found in pebbles, etc., from tributaries. 



He next describes other specimens of antigorite serpentine, examined 

 since 1905 ; some from New Zealand, kindly sent to him by Dr. J. M. 

 Bell, and others obtained in the Saasthal, especially from the Langefluh ; 

 giving further particulars about specimens in the National Collection 

 at South Kensington and in the University Collection at Cambridge. 



He then discusses the origin of the mineral. Pressure is apparently 

 essential ; certainly it can be formed from augite, and, though he has 

 not discovered residual olivine in his own rather numerous specimens, 

 or typical antigorite in Alpine bastite serpentines, he finds indirect 

 evidence of its coming from this mineral, proofs of which are given 

 by P. Becke, M. Preiswerk, and J. M. Bell. If, however, we suppose 

 the former existence of two types of peridotite in the Alps, as at the 

 Lizard and in the Vosges, and pressure sometimes to have preceded, 

 sometimes to have followed serpentinization, we can account for the 

 apparent conflict of evidence. 



2. "The St. David's Head 'Rock Series' (Pembrokeshire)." By 

 James Yincent Elsden, B.Sc, P.G.S. 



The St. David's Head and Carn Llidi intrusions are of complex 

 composition, ranging from a basic biotite-norite to an acid quartz- 

 en statite-diorite, and finally to soda-aplite. Throughout all the types, 

 except the last, there is a high magnesia percentage. The extreme 

 types sometimes pass abruptly one into the other, and at other times 



