518 Proceedings of the Royal Society 
to for an explanation of the structure of coral reefs are proximate, 
relatively well known, and continuous in their action. 
The author expressed his indebtedness to all his colleagues, to 
Professor Geikie, to the Hydrographer and officers of the hydro- 
graphic department, and in a special manner to Sir Wyville 
Thomson, under whose direction and advice all the observations 
had been conducted. 
Business. 
The following candidates were balloted for, and declared duly 
elected Fellows of the Society: — Major-General Bayly, R,E. ; Mr 
W. J. Solla/Sj M.A. ; and Mr Henry Drummond, F.G.S. 
Monday, 19 th April 1880. 
Sir WYVILLE THOMSON, Vice-President, in the Chair. 
The following Communications were read 
1. Rock- Weathering, as illustrated in Edinburgh Churchyards. 
By Professor Geikie, F.R.S. (Plate XVL) 
Comparatively little has yet been done in the way of precise 
measurement of the rate at which the exposed surfaces of different 
kinds of rock are removed in the processes of weathering, A few 
years ago, some experiments were instituted by Professor Pfaff of 
Erlangen to obtain more definite information on this subject. He 
exposed to ordinary atmospheric influences carefully measured and 
weighed pieces of Solenhofen limestone, syenite, granite (both rough 
and polished), and bone. At the end of three years he found that 
the loss from the limestone was equivalent to the removal of a 
uniform layer 0 S 04 mm. in thickness from its general surface. The 
stone had become quite dull and earthy, while on parts of its surface 
fine cracks and incipient exfoliation had appeared.* The time 
during which the observations were continued was, however, too 
brief to allow any general deductions to be drawn from them as to 
the real average rate of disintegration. Professor Pfaff relates that 
during the period a severe hail storm broke one of the plates of 
stone. An exceptionally powerful cause of this nature might make 
* Allgemeine Geologie als exacte Wissenschaft, p. 317. 
