On some Sections in the Glacial Deposits at Henclon. 139 



Oolitic Marl. 



Lower Freestones. 



Pea Grit. 



Transition Beds resting on Upper Lias. 

 The strata are described, and the results of microscopic examination 

 of the different beds given. These latter confirm the author's 

 views as to the important part which Girvanellm have taken in the 

 formation of oolitic granules ; whilst an examination of the borings 

 referred to by Prof. Judd in the discussion of Mr. Strahan's paper 

 " On a Phosphatic Chalk " convinces the author that these have no 

 connexion with the genus Girvanella. 



In the second part of the paper the insoluble residues left after 

 treating the various deposits with acid are considered. They contain 

 chiefly detrital quartz, felspars, zircons, tourmaline, chips of garnet, 

 and occasionally rutile. In the argillaceous beds silicate of alumina 

 was found to occur plentifully. The detrital material is considered 

 to be due to denudation of crystalline felspathic rocks, and not of 

 stratified ones. This view seems to be supported by the quantity 

 of felspar and its good state of preservation. 



The paper concludes with a consideration of the quantity of 

 residue and the size of the quartz-grains in the different deposits, 

 which are summarized in the following table : — 



Percentage Size of 



of Residue. quartz-grains, 

 in millim. 



Ragstones 2-8 -17 



Upper Freestones 1*1 *12 



Oolitic Marl S'2 -09 



Lower Freestones 1-8 -13 



Pea-Grit Series ,rO -14 



Transition Beds 38 - 3 -13 



This shows a great falling-off in the percentage of residue above 

 the Transition Beds. That of the Freestones is remarkably low, and 

 it would appear that these rocks were formed under conditions which 

 allowed of very little sediment being deposited. 



May 27. — Dr. A. Geikie, F.R.S., President, in the Chair. 

 The following communications were read : — 



1. " On the Lower Jaws of Promptodon" By R Lydekker, Esq., 

 B.A., F.G.S. 



2. " On some recently exposed Sections in the Glacial Deposits 

 at Hendon." By Henry Hicks, M.D., F.R.S., Sec. Geol. Soc. 



In this paper the author brings forward evidence obtained from 

 sections exposed in gravel-pits and deep cuttings made for the pur- 

 pose of laying down the main sewers, to show that Glacial deposits 

 had been spread out to a much wider extent over the Hendon 

 plateau than had hitherto been supposed, and that they had reached 

 down the slopes to below the ordnance-datum line of 200 feet. He 



