582 
Almanaque Nautico para el aoo 1863. Calculado de orden de 
S. M. en el Observatorio de Marina de la Ciudad de S. Fer- 
nando. Cadiz, 1861. 8vo . — From the Director of the 
Observatory. 
Pocket Diagram of Mean Pressures of Expanding Steam. By 
W. J. Macquorn Rankin, C.E., LL.D . — >From the Author. 
London University Calendar for 1862. 12mo . — From the Uni- 
ersity. 
Monday , 21 st April 1862. 
Professor CHRISTISON, Y.P., in the Chair. 
The following Communications were read : — 
1. On the Theory of Numbers. By H. Fox Talbot, Esq. 
2. On the Carboniferous Volcanic Rocks of the Basin of the 
Forth. By Archibald Geikie, Esq., F.R S. 
After referring to a previous communication to the Society, in 
which the author had given an outline of the chronology of the 
igneous rocks of Scotland, he proceeded in the present paper to de- 
scribe in detail the character of the volcanic phenomena in one dis- 
trict — that of the carboniferous system of the Forth basin. The 
igneous rocks of this district consist partly of doleritic and felspa- 
thic lava-form masses, and partly of various kinds of ash or trap- 
tuff. These materials present a considerable diversity in their modes 
of arrangement. But the author bad found that all the volcanic 
hills of the district might be reduced to three types of structure : — 1. 
A simple cone of ash, round and over which the ordinary sedimen- 
tary accumulation of the carboniferous period had been deposited. 2. 
A cone of ash with the crater filled up by a neck or plug of basalt. 
3. Sheets of different lavas with intercalated ash or sedimentary 
matter. 
He described in detail the succession of volcanic phenomena in 
the Lothians and in Fife, pointing out how local and limited the 
eruptions had been as a whole. They were confined to the earlier 
half of the carboniferous period, no interbedded igneous rock having 
yet been found in the formations that overlie the carboniferous 
limestone. The whole of this district appears to have been dotted 
