192 SULPHUR SPRINGS AND MUD VOLCANOES. 



gas is produced much as in a lime-kiln ; and the fact that limestone 

 fragments are ejected from Vesuvius leaves no doubt that the material 

 exists where it can be calcined. 



As the mountain cools and contracts, small cracks appear about 

 its summit and its flanks. These are termed " fumeroles," and give 

 vent to steam and various vapours, which deposit brilliantly- coloured 

 crystals of salts, that are mostly soluble and are dissolved by rain. 



The decline in eruptive power, however, is gradual, and at a lower 

 level on the flanks of mountains new phenomena often appear, and 

 testify to the changed condition of the interior regions. 



Solfataras. This is especially seen in the formation of solfataras, 

 which are essentially hot springs wherein the dissolved acids decom- 

 pose the rock through which the water flows, so that a good deal of 

 mud is brought to the surface ; and as the sulphuretted hydrogen in 

 the water is decomposed, sulphur is deposited in the clay in nodular 

 masses. Such sources of sulphur-supply occur at the solfatara near 

 Naples, and in the deposits near Girgenti in Sicily, and in Iceland. 

 Professor Ansted described some remarkable deposits and solfataras 

 at Kalamaki, near the Isthmus of Corinth, where the sulphur-bearing 

 region is about a mile long and half a mile wide. Not only are the 

 marls loaded with sulphur, but it is deposited in a crystalline form 

 from hot vapour, in gorges and caverns. 1 



Mud Volcanoes and Mud Springs. Another phase of declining 

 volcanic activity is exhibited in the formation of mud cones, which 

 are common not only in the volcanic regions of Mexico and Peru, but 

 in Iceland, and many localities in the South of Europe. Professor 

 Ansted mentions a mud eruption which took place in a flat plain 

 below Paterno, to the south-west of Etna, which threw out water in 

 strong jets, without visible vapour, though large bubbles of carbonic 

 acid gas arose through the muddy water. The temperature of the 

 water at the surface was 110 F. The fluid ejected was a thin mud, 

 which on exposure became a tenacious paste. A good deal of petroleum 

 floated on the surface of the water, and the neighbouring volcanic 

 rocks contain cavities full of naphtha, and have a strong bituminous 

 odour. Mud volcanoes are much more numerous on the eastern side 

 of the Crimea, reaching for about 50 miles from the straits of Kertch. 

 The cones about Yenikale pour out mud slowly from the top. The 

 fluid has a temperature of from about 55 to 65 F. It is tenacious, 

 often as thick as treacle ; and the streams, which are blackish when 

 dry, sometimes run for about 120 feet. The largest hill, near Kertch, 

 is about 250 feet high; and the main cone consists of clay, in which 

 are embedded small angular pieces of limestone and fragments of 

 earthy oxide of iron. 2 Other examples occur in North Italy, in 

 Parma and Modena. But among the most interesting are those dis- 

 covered by Captain Stifle 3 on the Mekran coast, which stretches 



1 Ansted, Q. J. G. S., vol. xxix. p. 360 ; and Th. Fuchs, Verb. K. K. Geol. 

 Reichsanst : 1876, p. 54. 



2 Royal Institution, Friday, May 1 1, 1866. 



3 Quart. Jour. Geol. Soc., vol. xxx. p. 50. 



