6&2 Geological Society : — 



of light by a system of centred spherical surfaces " are given in 

 appendices, followed by a very complete and valuable index of 

 both volumes. ' Applied Optics ' is something more than a mere 

 translation or compilation. It is a practical work edited by one 

 who has a complete grasp of the essentials necessary for the clear 

 presentment of this subject. The merit of this work is largely 

 due to the fact that it deals in a thorough and systematic way 

 with the principles and methods required in solving the problems 

 of the optical workshop. The editor and publishers are to be 

 congratulated on the appearance of this treatise, which will 

 remove to some extent the reproach that the study of technical 

 optics has made comparatively little progress in this country. 



LXIX. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 500.] 



January 22nd, 1919.— Mr. G. W. Lamplugb, F.R.S., President 

 in the Chair. 



HPIIE following communications were read : — 



1. ' On the Occurrence of Extensive Deposits of High-Level 

 Sands and Gravels resting upon the Chalk at Little Heath, near 

 Berkhamsted.' By Charles Jesse Gilbert, F.G-.S.. 



In a pit recently opened at Little Heath Common on a plateau 

 of the Chiltern Hills, 550 feet above sea-level, the following section 

 has been developed : — 



Thickness in feet. 

 6. Surface soil with bleached flint-pebbles from the 



Reading Beds about 2 



5. Pebbly clay and other Glacial deposits, varying 



from 2 to 20 



4. Stratified loamy sand 5 to 6 



3. Stratified coarse gravel 17 



2. Dark clay, with black-coated unworn flints and 



small well-rounded pebbles 6 inches 



1. Chalk. 



The upper Glacial deposit is a pebbly clay. The pebbles, which 

 are nearly all bleached and highly waterworn, are derived from the 

 Heading Beds. The pebbles are ahnost always in a vertical posi- 

 tion, or highly inclined, some being crushed in situ. 



The clay matrix is tough and mottled, and the highly-coloured 

 tints of the clay leave little room for doubt that it has been 

 derived from the upper part. of the Beading Beds. 



