THE PROBLEM OF THE ANORTHOSITES 239 



solidation is altogether too close to permit one to consider remelting 

 an important factor. Remelting would almost certainly destroy- 

 all law and order in this matter. Harker has recently expressed a 

 belief to the contrary, pointing out that the remelting of a solidified 

 mass with basic material at the bottom and acid at the top might 

 take place from the bottom upward. 1 Possibly it might, and in 

 an undisturbed crust it would realize the common sequence of 

 intrusion, but in an earth's crust subject to faulting, folding, and 

 overthrusting it may be doubted whether any regularity would be 

 observed. Disturbance of the stratified mass would often put 

 some of the basic material on a level with or even on a higher 

 horizon than some of the acid material. The remelting of such a 

 disturbed mass would not give rise to any significant regularity in 

 the intrusive sequence. 



A CONSIDERATION OF THE CRITERIA FOR THE RECOGNITION OF 

 ONCE MOLTEN ROCKS 



If we pass in review the development of ideas concerning igneous 

 or once molten rocks we find them first clearly recognized in surface 

 lavas. It was natural that it should be so, for here we have rocks 

 that, judging from their relations to their surroundings, have evi- 

 dently flowed as a liquid, and that are being duplicated in flows 

 from active volcanoes at the present day. Then we find a few 

 coming to believe that other rocks, usually quite distinct in appear- 

 ance and occurring as deep-seated masses only bared by erosion, 

 really are made up of the same material, the difference in appear- 

 ance being principally due to the difference of conditions under 

 which solidification took place. After much controversy this belief 

 gains general acceptance, especially as a result of the accumulation 

 of facts proving the essential identity of these deep-seated masses 

 with volcanic flows. Originally, then, it was this correspondence 

 of plutonic rocks with volcanic rocks that gave geologists the right 

 to consider them once molten or igneous rocks. Simultaneously 

 with the development of this view numerous facts corroborative of 

 it accumulated, important among these being the manner in which 

 the plutonic masses sent tongues into the surrounding rocks, and 



1 Journal of Geology, XXIV. (19 16), 556. 



