434 BOWEX AND AUROUSSEAU FUSION OF SEDIMENTARY ROCKS 



1.53. Such selective action during fusion as is in evidence is mainly 

 connected with the size of grain rather than with the nature of the ma- 

 terial. The residual undissolved grains are the larger grains of practi- 

 cally all the minerals present, and the ready getting together of the finer 

 grains to effect mutual fluxing has evidently been the important factor 

 in facilitating fusion. Quartz and plagioclase are the more persistent, 



Figure 2. — Thin-section of fused Core, Montezuma M'ell Xumler 1 



Crossed nicols. The dark areas are glass, the bright patches undissolved grains of 

 quartz and plagioclase. Twinned plagioclase at center. 



as they are the larger grains, but the quartz is apparently not more per- 

 sistent than j)lagioclase. It is not impossible, however, that the very fine 

 so called clayey matter may be intrinsically more fusible. Occasional 

 small fragments of metallic iron from the pipe are to be found in the 



glass. 



