470 ORIGIN OP ERUPTIVE AND PRIMARY ROCKS. 



this magma, the excess of silica was merely separated as quartz. * 

 These two explanations must not be confounded with each other. 

 The surfusion of Fournet differs essentially from the viscosity of 

 Durocher. ll En vertu du premier," says the latter philosopher, 

 " une substance peut conserver sa parfaite liquidity, a une tem- 

 perature inferieure a son point de fusion. En vertu du second) 

 des substances diverses, chauffe*es jusqu'a liquefaction, puis abannon- 

 n6es au refroidissement spontanne, dans les memes circonstances, 

 mettent des temps fort inegaux a se solidifier, celles qui tendent a 

 crystalliser, deviennent solides les premieres ; celles qui constitu- 

 ent des masses amorphes restent longtemps dans un £tat plastique 

 analogue a celui de la poix et interme'diaire entre l'e*tat liquide et 

 l'e'tat solide."f When we take into consideration the common 

 blowpipe reaction, in which silica is often separated from a fused 

 bead as a gelatinous skeleton, it would appear to lend consider- 

 able support to Durocher's theory. 



I here conclude the explanation which I have attempted of 

 the origin of the Primitive formation. I conceive that only one 

 series of rocks is entitled to this appellation. The term primary 

 has often been applied to quartzites and slates of later age ; which 

 rocks have been classified by German geologists under the name 

 of the Primitive Slate formation. It is very evident, however, that 

 there can have been but one primitive formation, and since the 

 slates and quartzites above referred to bear evidence of their having 

 been derived frem pre-existing rocks, it would appear incorrect to 

 entitle them primary or primitive. Were it not that geological no- 

 menclature is already sufficiently confused, it would appear much 

 more reasonable to apply the old term of Transition Formation to 

 these rocks ; since it is highly probable that during the period in 

 which they were formed, the temperature of the first crust gradu- 

 ally decreased to a temperature at which it was possible for water 

 to exist in large quantity on the earth's surface. We have seen 

 that during the first granitic eruptions, water did not exist on the 

 surface, otherwise rocks of a more or less tufaceous character would 

 have been produced. This conclusion would also seem to be cor- 

 roborated by the ideas which we must entertain of the high tem- 

 perature of the newly solidified crust. When the temperature of 

 the latter so far decreased as to admit of the condensation of the 

 water existing in the atmosphere, the rain, which fell upon it, must 



* Naumann, Lehrbuch, i., p. *?40. 



f Bui. de la Soc. Geol. 1849-50, p. 276. 



