BURNING CLIFF OF WEYMOUTH. 



275 



volcano broke out near the city of Mecca some centuries after iis 

 submission to the Mahometan faith. Extinct volcanoes are trace- 

 able in the vicinity of Mount Sinai, and from thence to the Dead 

 Sea. The indications of volcanic action in Persia, and in various 

 parts of the Asiatic continent, are too numerous to be cited : some of 

 the mountains far removed from the sea still emit smoke and vapour. 



Pseudo-Volcanoes. — To the accidental combustion of beds of coal, 

 the Germans have given the name of Pseudo-Volcanoes. There 

 are instances of coal mines having been on fire for many years ; but 

 they are too limited in extent or activity, to bear any comparison 

 with volcanic fires. Near Bilston in Staffordshire, there are coal 

 mines which have been continually burning for a long period ; the 

 effect of the fire on the beds of clay deserves notice, as it converts 

 them into a substance resembling jasper. 



There have been instances of portions of the cliffs of England 

 taking fire spontaneously, and burning for a considerable time : this 

 is, at present, the case in a cliff near Weymouth. In the last cen- 

 tury, after a hot summer, and heavy rains, the cliff near Charmouth 

 in Dorsetshire took fire, and continued burning for several months. 

 When portions of the cliffs near Whitby in Yorkshire fall upon the 

 beach, and become moistened, they are sometimes spontaneously ig- 

 nited. The same effect takes place in the Staffordshire coal mines; 

 when parts of the bed of indurated clay which forms the roof of the 

 coal fall down, and become moistened, it takes fire spontaneously : 

 and hence this combustible clay is provincially called tow. 



All these instances of spontaneous combustion admit of a satisfac- 

 tory explanation. The cliffs of Charmouth and Whitby are com- 

 posed of lias clay, much intermixed with bituminous and carbona- 

 ceous matter, and the sulphuret of iron, (iron pyrites :) such is also 

 the composition of the inflammable clay which forms the roof of the 

 coal in Staffordshire ; and the clay which forms the cliffs near Wey- 

 mouth is similar in composition to the lias clay of Charmouth and 

 Whitby, though it belongs to an upper part of the secondary strata. 

 Iron pyrites abound in these cliffs ; and it is a well known property 

 of this mineral, to decompose rapidly, when laid in heaps and moist- 

 ened with water. During this rapid decomposition, sufficient heat is 

 evolved to ignite the bituminous matter in the clay: and the clay, 

 when once ignited, will burn for a long period; — this is proved in the 

 process employed for making alum at Whilb}^ There can be little 

 doubt that this spontaneous combustion might be imitated, artificially, 

 by mixing pyrites and bituminous clay or shale, and moistening the 

 heap with water. The experiment of Lemery is well known : he 

 mixed twenty five pounds of powdered sulphur with an equal weight 

 of iron filings ; and, having made with water a paste of the mixture, 

 he put it into an iron pot covered with a cloth, and buried it a foot 

 under ground. In about eight hours, the earth swelled and cracked, 

 and hot sulphureous vapours were exhaled ; a flame was observed 



