On the Formation of Pegmatite- 43 



and a saturated aqueous solution a large number of con- 

 secutive intermediate stages can be imagined. In this way, 

 it seems to me, the connection between the pegmatitic 

 veins and the ordinary granites, the remarkable segrega- 

 tions in the shape of pegmatitic veins opening out into 

 druses, and finally the connection of these with vein-fillings 

 which consist only of quartz, tourmaline and potash mica, 

 or of quartz alone, can be explained," etc., etc. 



On the whole I must agree with Lehmann. since he 

 considers the pegmatite veins as true injection veins, erup- 

 tive veins., formed in essentially the same way as the granite 

 itself; in his peculiar speculations upon the special condi- 

 tions under which the plu tonic rocks have been formed, I 

 cannot agree with him in everything. He assumes for in- 

 stance (1. c.j p. 54) a relatively low temperature for the 

 original granitic magma, (about 500° C.j, because in the 

 minerals of the granite no glass inclusions nor any attend- 

 ant phenomena of corrosion have been recognised. This, 

 however, is no evidence against a high temperature of the 

 granitic magma, as the formation of glass is dependent 

 naturally upon rapid cooling, which at the relatively great 

 depths at which the magmas would solidify to granites, 

 etc., is not possible. The strict connection of extruded 

 eruptive masses with plutonic rocks l which is now known 

 in many localities, would, according to Lehmann's hypo- 

 thesis, lead to the remarkable result, that an eruptive 

 magma, solidifying at a great depth, must have possessed a 

 much lower temperature than the same magma solidifying 

 at the surface ; the extrusion of a magma must, therefore, 

 have been accompanied on its upward way to the surface 

 by an extraordinary increase of temperature ! The depth, 

 too, which Lehmann assumes as the horizon of granitic 

 solidification is more or less conjectural. "It is not impos- 

 sible that a line of fissure some 35 km. in length, such as 

 that of the principal line of fracture in the Saxon granulite 



1 For granite rocks, for example, K. Dalmer's work " Die Quarztrachyte von 

 Campiglia," etc., Neues. Jahrb. 1887, 2, 206-221, may be consulted. In the 

 Christiania district I know excellent examples (for instance, tie series of augite 

 syenite to rhombic porphyry, with glassy enclosures in the apatite needles), etc. 



