194 



THE GEOLOGIST. 



List of Books, Memoirs, &c. 

 ^.—"Observations on the Wrekin," &c. Geol. Trans. 1 ser., vol.1., 

 p. 191. 



Aveline, W. T.—See Ramsay. 



Barrande, J. — " Le Bassin Silurien de Boheme " {TriloUtes). 18. 



„ "Graptolites de Boheme." Prague, 1850. 



Bowman, J. E. — On a small patch of Silurian Rocks, to the west of Abergele, &c., 

 Geol. Proc, Vol. II., p. 666 ; Transact. 2 ser. Vol. VI., p. 195. 

 <' Notice of Upper Silurian Rocks," &c., Trans. 3Ianch. Geol. Soc, 

 Vol. I., p. 194 



Davidson, T. — " Observations on Wenlock Limestone Brachiopoda." London 

 Geol. Pal. Journ., Vol. I., p. 1. 

 „ Les Brachiopodes du Systeme Silurien sup. d'Angletere." Bull, 



de la Soc. Geol. de France, 2 ser. Vol. 5, p. 309. 

 „ "On^^bolus. Brit. Foss. Brach, 1854. Introduction, p. 135. 



Davis, J. E. — " On the Geology of Tremadoc," &c. Jour. Geol. Soc, Vol IL p. 70. 

 De la Beche, Sir H. T. — " On the Formation of the Rocks of South Wales," &c. 



Mem. Geol. Survey, Vol. I. 

 Edward, M.,Q.u^ J. Haime. — "Polyp, foss. des Terr. Paleoz." Arch, du, Mus. v. 5. 



,, " British Fossil Corals." Palceonto graphical Soc. 



Fitton, Dr. W. H. — " The Silurian System." Edinburgh Revieu\ April, 1841. 

 Forbes, E. — "On the Cystidea of the Silurian Rocks." 3Iem. Geol. Surv., Vol. II. 

 p. 483. 



,, " On Fossil species of Creseis. " Jour. Geol. Soc, Vol. I., p. 145. 

 „ " On Oldhamia." Duhin Geol. Jour., Vol. IV., p. 20. 



{To he continued.) 



FOREIGN COREESPOT^DENCE. 

 By De. T. L. Phipson, oe Paeis. 



Origin of the mud in these volcanos — Rarity of Sulphate of Potash in 

 nature — Alundance of sulphate of soda — Beds of this salt in Spain. 



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 volcanos, 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., are entirely wanting in some 

 volcanos, 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 



