462 WHITMAN CROSS 



of the rock which the investigator judges was in a fluid or pasty- 

 condition at the beginning of the second period of consolidation 

 — the " pate." 



Samuel Allport. — During this period in which Zirkel, Rosen- 

 busch, Fouque and Michel-Levy were formulating more or less 

 distinct advances in systematic petrography, the English students 

 of rocks made but slight positive contributions in this direction. 

 The condition of the science may be best appreciated by reference 

 to the various short discussions of principles of classification by 

 Samuel Allport. This careful investigator often pointed out the 

 fallacy of the age distinction, so clearly illustrated by the long- 

 known ancient lavas of the British Isles, and also the importance 

 of Judd's discovery of the intimate relationship of coarsely crys- 

 talline and volcanic rocks. This was cited to disprove the idea 

 that a sharp line could be drawn between the Plutonic and Vol- 

 canic rocks. But Allport considered it premature to suggest 

 any great changes either in classification or nomenclature. 



Claretice King, i8j8. — In America no original contributions 

 to systematic petrography were made prior to the microscopical 

 period. The earliest use of the knowledge gained in that period 

 was probably by Clarence King, 1 whose appreciation of its value 

 led to the report upon the Microscopical Petrography of the 40th 

 Parallel rocks by Zirkel, and who, also, applied certain sup- 

 posed facts resulting from microscopical research in his own 

 discussion of the classification of volcanic rocks. The propo- 

 sition referred to has had little influence upon petrographic 

 system, but has a certain importance from the standpoint of this 

 review as illustrating again the dangers of applying genetic ideas 

 in the classification of igneous rocks. 



King accepted the law of Bunsen and the law of succession 

 of volcanic rocks advocated by von Richthofen, which have been 

 stated. He also considered that " a sharp line is to be drawn 

 between the so-called Plutonic rocks and the true igneous ones." 

 The microscopical studies of which he had knowledge led him 



1 Report of the Geological Exploration of the Fortieth Parallel, I. Systematic 

 Geology, pp. 705-25, Washington, 1878. 



