4 DEVELOPMENT OF PETROLOGY. 



all petrologists, and in many respects supplied a long felt 

 want. 



The amount of criticism levelled at this scheme since 

 its inception has been considerable, and its adoption by 

 the Americans has been more pronounced than by others. 

 Petrologists have been seeking for a truly natural classifica- 

 tion of igneous rocks, and perhaps the main objection 

 to the American classification is that it is not a natural one. 



The year 1903 was an important one, as several works 

 of great value were issued. Two important memoirs were 

 published by Vogt, of Christiania, " Die Silikatschmelzlo- 

 sungen," I. and II., and therein he gave his results of 

 certain experiments upon slags, and fused silicates, and 

 showed how the laws of solution may be applied to the 

 cyrstaUization of igneous rock-magmas. The results of 

 researches by Doelter and Ebelmen were also availed of 

 by Vogt in his deductions. Vogt applied the principles 

 of physical chemistry with great success and acted in this 

 way : — Slags of rock-magmas are believed to be solutions ; 

 their constituents are known ; one can therefore proceed 

 to experiment "svith their constituents and to predict the 

 behaviour of their mixture according to the principles 

 of physical chemistr3\ 



Vogt made the first comprehensive attempt to apply 

 the principles of solutions to the crystallization of the 

 igneous rock-magmas and even for that alone Petrology 

 owes him a great deal. 



In this year "" A Treatise on Metamorphism,'" by 

 C R. Van Hise, was published as Monograph XL VII, 

 U.S. Geol. Survey. This is a treatise of monumental 

 proportions and is really an attempt to reduce the 

 phenomena of metamorphism to order under the principles 

 of physics and chemistry. Van Hise took seven years 

 in actually preparing this work and he advanced the know- 

 ledge of metamorphic rocks and the conditions of their 

 formation very extensively indeed. 



The first of a series of papers by R. A. Daly on the 

 " Mechanics of Igneous Intrusion," was published in this 

 year. In this first paper Daly concluded that dykes, sheets, 

 laccolites, bysmaliths, and perhaps a few of the smaller 

 stock-like plutonic bodies are conceived to be due to crustal 



