108 NEWER PLIOCENE PERIOD. [Ch. IX. 



into tuffs and pcperinos, nor can we imagine that, under 

 enormous pressure, they could have become porous, since we 

 observe, that the lava which has cooled down under a moderate 

 degree of pressure, in the dikes of Etna and Vesuvius, has a 

 compact and porphyritic texture, and is very rarely porous or 

 cellular. No signs of volcanic sand, scoria^ breccia, or conglo- 

 merate are to be looked for, nor any of stratification, for all 

 these imply formation in the atmosphere, or by the agency of 

 water. The only proofs that we can expect to find of the 

 successive origin of different parts of the fused mass, will be 

 confined to the occasional passage of veins through portions 

 previously consolidated. This consolidation would take place 

 with extreme slowness, when nearer the source of volcanic heat 

 and under enormous pressure, so that we must anticipate a 

 perfectly crystalline and compact texture in all these subter- 

 ranean products. 



Now geologists have discovered, as we before stated, great 

 abundance of crystalline and unstratified rocks in various parts 

 of the globe, and these masses are particularly laid open to our 

 view in those mountainous districts where the crust of the earth 

 has undergone the greatest derangement. These rocks vary 

 considerably in composition, and have received many names, 

 such as granite, syenite, porphyry, and others. That they 

 must have been formed by igneous fusion, and at many distinct 

 eras, is now admitted ; and their highly crystalline texture is 

 such as might result from cooling down slowly from an intensely- 

 heated state. They answer, therefore, admirably to the condi- 

 tions required by the above hypothesis, and we therefore deem 

 it probable that similar rocks have originated in the nether 

 regions below the island of Sicily, and have attained a thickness 

 of from one thousand to three thousand feet, since the newer 

 Pliocene strata were deposited. 



It is, moreover, very probable, that these fused masses have 

 come into contact with subaqueous deposits far below the sur- 

 face, in which case they may, in the course of ages, have greatly 



