142 Reports and Proceedings — Geological Society of London. 



(4) The Infratrappean Grits are maintained to be superficial 

 deposits on the pre-trappean land-surface, some being the ordinary 

 results of weathering, others due to the washing down of debris to 

 a water-covered level, and others again simply seolian drift. It is 

 thus seen that there has been constancy in the meteorological 

 conditions of Cutch from recent times as far back as the Cretaceous 

 period. 



(5) The Laterite-deposits of the district occur to a height of only 

 120 feet above the Eann. There is evidence that they were laid 

 down in water at a time when the surface of the country was not 

 very different from the present one. The material may have been 

 partly derived from Jurassic rocks, but some of the constituents, as 

 the eroded agates, must have come from the trap-rocks. 



(6) The Rann is an area which has recently been abandoned by 

 the sea, owing to unequal movements, but there is evidence that 

 deposit has also taken place in it, and the depression has become 

 shallower, so that in course of time the whole surface will be made 

 of alluvial or ^olian soil. 



III._February 24, 1897.— Dr. Henry Hicks, F.R.S., President, 

 in the Chair. The following communications were read : — 



1. " On the Nature and Origin of the Rauenthal Serpentine." 

 By Miss Catherine A. Raisin. B.Sc. (Communicated by Professor 

 T. G. Bonney, D.Sc, LL.D., F.R.S., V.P.G.S.) 



This serpentine has been already described by Herr Weigand as 

 one of those which occur in regions of gneiss or schist related in 

 their origin to those rocks. In order to test this hypothesis as to 

 the formation of the serpentine, the author has examined the district, 

 and has studied its rocks with the microscope, 



Herr Weigand asserted that transitions could be recognized from 

 typical gneiss to a peculiar amphibolite, and that the latter rock has 

 been changed to serpentine. The author could find in the field no 

 evidence of a passage from gneiss to amphibolite, and calls attention 

 to the general difficulty of the supposition. She states that when 

 the serpentine is examined microscopically, the greater part shows 

 the usual appearance of serpentine derived from olivine, and can be 

 distinguished from included parts, which have resulted from change 

 in hornblende or other pyroxenic constituents. Further, that 

 several accessory minerals occur which are usually found in 

 peridotites. The rock also contains a peculiar chlorite. This she 

 thinks the result of the modification of a biotite, for the latter 

 mineral occasionally occurs as a constituent in a neighbouring 

 serpentine, and both there and in the Rauenthal, intermediate forms 

 apparently can be detected. It seems to her that the chemical 

 analyses already published are not in harmony with the supposed 

 change of a hornblende rock into serpentine. 



While it is true that a hand-specimen sometimes shows a transition 

 (generally rapid) from a rock consisting mainly of hornblende to 



