6 THE JOURNAL OF GEOLOGY. 



rarity in Mesozoic times. It is, however, also connected with 

 the Wernerian doctrine of the non-recurrence of certain physical 

 conditions in the earth's development, as contrasted with the 

 uniformitarianism of Hutton and Lyell. The absence of vol- 

 canic types in Europe which serve to bridge over the sharp 

 contrast between those of the Carboniferous and Tertiary, 

 is being rapidly compensated by the discovery of such rocks in 

 other regions. Fortunate finds of even pre-Cambrian lavas so 

 perfectly preserved as to demonstrate their practical identity, 

 both chemically and structurally, with recent products is tending 

 to weaken the old distinction on the continent. There are now 

 many signs of progress toward the idea that the characters 

 regarded as belonging peculiarly to the older effusive rocks are 

 better explained through changes subsequent to their solidifica- 

 tion. 



Thus Ludwig in i86i,^ Vogelsang in 1867,^ and Lossen in 

 1869,3 regard some quartz-porphyries as only devitrified glasses, 

 identical with those of modern volcanic regions ; Kalkowsky,'^ 

 and recently Sauer 5 and Vogel,^ have also brought convincing 

 proof that such is often the case. 



Giimbel says: "Es scheint in dieser Beziehung denn doch eher gerecht- 

 fertigt, zunachst das petrographisch Gleiche auch gleich zu bezeichnen, als in 

 einzelnen Fallen ein neues Princip, das des Alters, in die Petrographie einzu- 

 fiihren, welches bei den meisten iibrigen Fallen nicht verglichen und beriick- 

 sicht werden kann ; " ^ 



And Rosenbusch also remarks : 



" Man hat den geologischen Alter der Eruptivgesteine bisher ein hoheres 

 bestimmendes Moment fiir die structurelle und mineralogische Ausbildung 

 dieser zugeschrieben als demselben in Wirklichkeit zukommt."* 



^ Erl. z. geol. Karte Hessens, Bl. Dieburg, p. 56, 1861. 



^ Philosophie der Geologic, pp. 144-146, 1867. 



3Abh. Berl. Ak., 1869, p. 85. 



" Tschermak's Min. Mitth, pp. 31 and 58, 1874. 



5 Erl. zur geol. Specialkarte Sachsens, Bl. Meissen, pp. 81-91, 1889 



* Abh. geol. Landesanstalt von Hessen, vol. ii., p. 38, 1892. 



7 Grundziige der Geologie, 1888, p. 85. 



^Die massigen Gesteine, 2d. ed., 1887, p. 4. 



