Volcanos and Earthquakes. 63 



the strata of the Neptunian rocks. Granites have been forced 

 up to the surface at the most widely different periods ; we find 

 them most commonly in clay-slate, and in the greywacke for- 

 mation, in gneiss and in mica-slate, and they are sometimes con- 

 nected with other more considerable masses of granite. Even 

 after the formation of the oolitic and chalk groups, they have 

 been ejected; but there are no granitic dykes described as 

 intersecting these rocks. The stratified rocks are usually al- 

 tered in the immediate vicinity of masses or dykes of granite ; 

 and their stratification becomes indistinct and confused. The 

 porphyries, like the granites, exist as independent formations ; 

 but these are not so frequent or so extensive, and are more fre- 

 quently in contact with more recent stratified formations than 

 the granites. The trap rocks traverse all the stratified rocks 

 from the gneiss and greywacke group, at least to the oolites in- 

 clusively. The basalts are found in all formations, from the 

 transition and secondary rocks to the bgnite inclusively, nay, 

 in the nexyest formations.* 



In general, some alteration in the adjacent rock and some 

 new mineral production s,t are found where such masses have 

 been forced up, and large and small fragments of the rock are 

 not uncommonly found firmly imbedded in the latter. We may 

 here, by way of example, mention the conversion of compact 

 limestones into marble, exactly as Hall changed limestones by 

 heating them in close vessels or under pressure ; and again, the 

 disappearance of the black colour and the bitumen in the coal- 

 sandstone.j 



* Leonliard's Basalt Gebilde t. ii. p. 6, &c. 



+ The adjacent rock, heated by the melting mass, might, by their both 

 cooling very slowly together, give rise to the production of crystalline sub- 

 stances (as hornblende, felspar, mica, by the contact of gi-anite with clay- 

 slate). But the rock would probably also take up substances from the melting 

 mass (alkalies) which Avould serve as a flux. 



Z The combustion of beds of brown coal seems also to have been effect- 

 ed by igneous fluid masses which had risen from the interior. Thus the 

 remains of such combustions always occur in Bohemia^ according to Dr 

 lleuss (Noggerath Ausflug nach Bohmen. Bonn. 1838, p. 171), in the neigh- 

 bourhood.of basalts, and these plienomena are so enormous, that they can- 

 not be considered as caused by accidental combustions. 



