Ndtural History of Volcanos and EarthquaTces. 265 



also found in positions which shew that they must have risen 

 from the interior of the earth, after the formation of the stratified 

 rocks, and found their way into fissures, which in many cases do 

 not reach the surface. Thus, granite, syenite, trachyte, the por- 

 phyries, the greenstone, and so on, up to the basalts, form dykes 

 in the stratified rocks as well as in one another. They also not 

 unfrequently appear in beds between the strata of the Neptunian 

 rocks. Granites have been forced up to the surface at the most 

 widely difl^erent periods ; we find them most commonly in clay- 

 slate, and in the greywacke formation, in gneiss and in mica- 

 slate, and they are sometimes connected with other more consid- 

 erable 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 stra- 

 tified rocks are usually altered in the immediate vicinity of masses 

 or dykes of granite ; and their stratification becomes indistinct 

 and confused. The porphyries, like the granites, exist as inde- 

 pendent formations ; but these are not so frequent or so exten- 

 sive, and are more frequently in contact with more recent stra- 

 tified formations than the granites. The trap rocks traverse all 

 the stratified rocks from the gneiss and greywacke group, at least 

 to the oolites inclusively. The basalts are found in all forma- 

 tions, from the transition and secondary rocks to the lignite inclu- 

 sively, nay, in the newest formations.* 



In general, some alteration in the adjacent rock and some new 

 mineral productions,! ^>^6 found where such masses have been 

 forced up, and large and small fragments of the rock are not un- 

 commonly 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 color and the bitumen in the coal sandstone.."]: 



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



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

 very slowly together, give rise to the production of crystalline substances (as horn- 

 blende, felspar, mica, by the contact of granite with clay-slate.) But the rock 

 would probably also take up substances froni the melting mass (alkalies) which 

 would serve as a flux. 



t The combustion of beds of brown coal seems also to have been effected by 

 igneous fluid masses which had risen from the interior. Thus the remains of such 

 combustions always occur in Bohcvda, according to Dr. Reuss, (Noggerath Ausflug 



Vol. XXXVI, No. 1.— April-July, 1839. 34 



