ORIGIN OP ERUPTIVE AND PRIMARY ROCKS. 355 



from the conflict of which with the fluid granite such rocks could 

 Result, At the time of these eruptions, therefore, the temperature 

 of the earth's surface must have been higher than the boiling point 

 of water, and the whole of the latter now condensed on the surface 

 must then have existed only in the atmosphere. 



With regard to the stratified varieties of granitic rocks it will 

 be seen from the above table, that such have been abundantly 

 developed. Even syenites occasionally possess parallel structure, as 

 is the case of those of the Plauensche Grund near Dresden, of Ullern- 

 Aasen, near Christiania, and of the Odenwald. A banded struc- 

 ture has been observed in the syenites of Brotterode in Thurin- 

 gia, of Jurgojaskaja in Asiatic Russia, and of the Malvern Hills. 

 Phillips regards this structure, in the latter instance, as having 

 been produced during the original solidification of the rock.* He 

 remarks that " the laminar and banded structures may be regarded 

 as indications of crystallization under restraint, such restraint hav- 

 ing reference to particular planes in consequence of the pressure 

 of preconsolidated parts adjacent." One of the most important tran- 

 sitions observable among these rocks, however, is the stratification 

 of granite, whereby it gradually assumes the character of gneiss. 

 The most abundant and striking examples of this are to be found 

 in the Primitive Gneiss formation, where granite occurs in beds 

 between gneiss strata, and forms gradual but distinct transitions 

 into these, by the laminee of mica gradually arranging themselves 

 parallel to each other, and parallel to the direction of the strata 

 generally. But the irregular masses of granite to which we have 

 already referred have also often been observed to assume a slaty 

 structure as they approach the rocks adjoining them. One of the 

 most remarkable examples of this occurs in the Primitive Slate 

 formation of Upper Tellemarken in Norway,especially in the neigh- 

 bourhood of Aamdal, Vraadal, Hvideseid, &c. In the interior parts 

 of the granitic protrusion, the rock is thoroughly crystalline. 

 Towards its limits, gneissoid granite is developed, the foliation of 

 which is invariably parallel with the line of its junction with 

 the adjoining rocks. That the rock here referred to is decidedly 

 eruptive is proved by the numerous fragments of neighbouring 

 slate enclosed in it.f Instances of exactly the same phenomenon 

 have been observed near Taubenheim, in Saxony, and in the valley 

 of the Schwarza, in Thurin^ia. At the latter place the granite is 



* Mem. of the Geol. Survey of Great Britain, II. 1, p. 74. 

 t Dabll : Om Thelemarkens Geologie, p. 1. 



