THE EVOLUTION OF PETROLOCIICAL IDEAS. 298 



consolidation tho watci" would concentratt^ in tlic mother li(|U()r, and 

 ultimately m th(> silica. Final consolidation would take place on the 

 escape of tlie water. Thus tlu^ paradoxical ordei- ol' crystallization 

 would be explained, and the oranite nught consolidate at a temperature 

 which would admit of the formation of the pyronnomic nnnerals. 



The theory of 8cheer(>r was opposed by Durocher, and the contro- 

 versy between these two distinguished men extended over a period of 

 three or four years. Durochei" considered that a close exand nation 

 of th(^ structure of graniti*. does not bear out the view that there is a 

 well-defined order of consolidation. The minerals mutually interfere 

 one with the other, sometimes one and sometimes another having' the 

 advantage. The magma appears to have cooled down to a compara- 

 tivelv low temperature, and tlien to have separated into definite com- 

 pounds-which did not solidify instantaneously. Tln^ relative perfec- 

 tion of form would, on this view, be largely determined l»y the relative 

 power of crystallization of the different constituents. In this respect 

 quartz is at a disadvantage. It possesses, moreovcn-, as shown by M. 

 Gaudin, a great i-ange of viscosity, and when fused can be drawn into 

 threads like glass and sealing wax. He agrees with Sche(>r(U- in reject- 

 ing Fournet's theory of surfusion, and considers that the paradoxical 

 order of consolidation can be explained l)y taking into consideration 

 the wdde range of viscosity of (juartz and its slight t(Mid(Micv to crys- 

 tallize. A similar view has recently been advocated by Professor doly. 

 Durocher replies to Scheenn-'s argument derived from the absence of 

 (juartz in obsidians by pointing to its presence in trachytes, and 

 attempts, somewhat unsuccessfulh . to explain away th(> presence of 

 the pyrognomic minerals. In his criticisms of Scheerer's views as to 

 the amount of water present in granite he is often effective, for he 

 shows that sufficient allowance had not been made for the effects of 

 alteration. 



Scheerers view became the popular one, and is now generally held. 

 It was greatly strengthened by Dr. Sorby's discovery of the widespread 

 distribution of liquid ca\ ities containing water in the ([uartz of gran- 

 ites, and 1)}^ the well-known synthetic experiments of Daubree and 

 others. The failure of all attempts to produce granite is also still felt 

 to be a strong argument against the theory of dry fusion. 



Scheerer concludes the discussion with some obser^'ations which I 

 can not refrain from (pioting. He says: 



"To avoid misuiulerstanding, I desire to make; some remarks on the 

 value which I attacdi not only to my theory of the origin of granite, 

 but also to geological theories in general. I am far from believing 

 that the igneous theory, which M. Durocher defends with so nmch 

 vigor, is finally disposed of, or that my theory is completely satisfac- 

 tory. Such deffnite conclusions can not lie reached in the presiMit state 

 of our science. . More than one point of" view is possible on almost 

 every subject of this kind. ;uid thus it must ever b(\ for mathematical 

 certainty is unattainable. 



