Ch. XL] THE PRIMARY ROCKS. 221 



again, at successive eras, with the same characters, penetrating 

 the stratified rocks in different regions, and not always asso- 

 ciated with strata of the same age. Nor are organic remains 

 always wanting in the formations invaded by granite, although 

 their absence is more usual : granite so circumstanced has 

 been detected by Von Buch in Norway, by Macculloch in 

 Sky, and by Hugi and Elie de Beaumont in the Alps. In 

 such examples, however, we can merely affirm that the granite 

 is newer than the fossiliferous rock ; but can form no con- 

 jecture as to the precise period of its origin. It is, indeed, 

 very necessary to be on our guard against the inference that 

 a granite is usually of about the same age as the group of 

 strata into which it has intruded itself: for, in that case, we 

 shall be inclined to assume rashly, that the granites found 

 penetrating a more modern secondary rock, such as the lias 

 for example, are much newer than those found invading 

 strata older than the carboniferous series. The contrary may 

 often be true, for the Plutonic rock, which was last in a 

 melted state, may not have been forced up any where so near 

 the surface, as to enter into the newer groups of strata ; and 

 it may have been injected into a part of the earth's crust 

 formed exclusively of the older sedimentary formations. 



It has been stated that the primary rocks are divided into 

 two natural classes, the stratified and unstratified : the pro- 

 priety of the term stratified is justified by a careful com- 

 parison of the rocks so designated, with strata known to result 

 from aqueous deposition. If we examine, for example, gneiss, 

 which consists of the same ingredients as granite, or mica- 

 slate, we find that it is made up of a succession of beds, the 

 planes of which are, to a certain extent, parallel to each other, 

 but which frequently deviate from parallelism in a manner 

 precisely analogous to that exhibited by sedimentary form- 

 ations of all ages. 



Another striking point of resemblance between the stratifi- 

 cation of the crystalline formations, and that of the secondary 

 and tertiary periods, is the alternations in each, of beds 



