444 BOAVEN AXD AUROUSSEAU FUSIOX OF SEDIMENTARY ROCKS 



These rocks belong to the subrang tonalose, but inspection of this sub- 

 rang in Washington's tables shows that they differ in composition from 

 typical igneous rocks in the same way as the average shale differs from 

 the average igneous rock. In the closest general matches obtainable, 

 lime is distinctly higher and the ratio of soda to potash greater in the 

 igneous rocks. Moreover, were all the analyses in columns 1-4 of Table 

 lY reduced to 100 after excluding water, this divergence would be in- 

 creased. It was also evident, in our endeavor to match an igneous rock 

 with the Montezuma sediment, that the closer parallels were often 

 igneous rocks of unusual compositions, such as schliers in gTanites. In 

 matching the fused sediment from the Meyer well (see Table II) it was 

 found that most of the lassenoses resembling it showed higher figures 

 for MgO -[" C^'aO and a greater ratio for soda over potash. 



Gexeeal Coj^^sideratioj^s regardikTt THE Fusibility of Cores 



There is a very strong suggestion in the information gained from these 

 and other studied cores that arkose is particularly susceptible to the 

 fusing action here described. This is as it should be, for, contrary to 

 the common misconception, a mixture rich in alkaline feldspars and 

 quartz should constitute the most fusible material to be made up from 

 ordinary rock-forming minerals. Frequently one will find in the liter- 

 ature the statement that femic material fuses more readily than salic; 

 but this is due to the failure to distinguish between fusibility and fluidity. 

 It is true that femic material forms a more fluid melt than salic material, 

 but it is likewise true that a salic melt can be obtained at lower temper- 

 atures than can a femic melt. AVe refer here to anhydrous conditions, 

 not to the conditions obtaining in magmas where this contrast is further 

 emphasized by the fact that the salic magmas ordinarily contain more 

 volatile matter than do the femic. The greater fusibility of salic ma- 

 terial is well brought out in the studies of Sosman and Merwin on inclu- 

 sions of arkose in the Palisade diabase, which were found to fuse in the 

 laboratory at a temperature 100 degrees centigrade lower than the fusion 

 temperature of the diabase.^ 



Eefusiox of Sedimexts as a Factor ix Mag:ma Gexesis 



The arkosic nature of the sediment that was fused to form these cores 

 and the consequent close chemical approach of the cores to an igneous 

 rock are matters that require emphasis for another reason. Some geol- 



'= .T'MU". Wash. Acad. 8ci., vol. 3, 1913, p. 394. 



