194 
THE GEOLOGIST. 
List of Books, Memoirs, &c. 
Aikin, A. — "Observations on the Wi-ekin," &c. Geol. Trans. 1 ser., vol.1., 
p. 191. 
Aveline, W. T. — See Ramsay. 
Barrande, J. — " Le Bassiu Silurien de Boheme " (Trilohi/es). 18. 
,, " Graptolitcs de BoUijme.'' Prague, 1850. 
Bowman, J. E. — On a small patch of Silurian Rooks, to the west of Abergele, &c., 
Geol. Proc, Vol. II., p. 606 ; Transact. 2 ser. Vol. VI., p. 195. 
„ " Notice of Upper Silurian Rocks," &c., Trans. Munch. Geol. Soc, 
Vol. I., p. 194. 
Davidson, T. — " Observations on Wenlock Limestone Brachiopoda." London 
Geol. Pal. Journ., Vol. I., p. 1. 
„ " Les Brachiopodes du Systcme Silurien sup. d'Angletere." Bull, 
de la Soc. Gt-ol. de France, 2 ser. Vol. 5, p. 309. 
„ "OnAbolus. Brit. Foss. Brach, 1854. Introduction, p. 135. 
Davis, J. E. — " On the Geology of Tremadoc," &c. Jour. Geol. Soc, Vol II. p. 70. 
De la Becke, Sir H. T. — " On the Formation of the Rocks of South Wales," &c. 
Mem. Geol. Survey, Vol. I. 
Edward, M., and J'. Haime. — " Polyp, foss. des Terr. Paleoz." Arck. du, Mus. v. 5. 
„ „ " British Fossil Corals." Palaontograpliical Soc. 
Fitlon, Dr. W. H. — " The Silurian System. " Edinhurgh Review. April, 1841. 
Forbes, E. — "On the Cystidea of the Silurian Rocks." Mem. Geol. Surv., Vol. II. 
p. 483. 
,, " On Fossil species of Creseis. " Jour. Geol. Soc, Yo\. l.,i>. 1A5. 
„ " On Oldhamia." Dubin Geol. Jour., Vol. IV. , p. 20. 
(7b be continued.) 
FOKEIGN COERESPONDENCE. 
By Dk. T. L. Phipson, of Paris. 
Origin of the mud in these voleanos — Ra/rity of Sulphate of Potash in 
nature — Abundance of sulphate of soda — Beds of this salt in S2>ain. 
We have stated that the mud discharged in these eruptions derives its 
origin from the materials of the mountains themselves. It replaces the 
lava of ordinary voleanos, as we observe to be the case with other mud- 
erupting craters which emit little or no lava — ^for instance, those of 
South America. We also observe that vitreous volcanic formations, 
such as obsidian, pearl-stone, pumice, &c., ai-e entirely wanting in some 
voleanos, where compact or porous lava is the common product. 
Volcanic productions are, indeed, extremely variable, and differ ac- 
cording to the particular volcano to which they owe their birth. 
Humboldt informs us that the mineral composition of lava differs 
according to the nature of the crystalline rock of which the volcano is 
formed, the height of the point where the eruption occurs, and the 
temperature of the interior of the mountain. If we consider the 
marvellous production of minerals by the sole influence of water heated 
to 400° Centigrade, as related in one of our former papers — if we 
