SOSMAN AND MERWINI DATA ON PALISADE DIABASE 393 



are very fresh. The latter minerals and magnetite appear to 

 have originated chiefly from chloritized biotite originally present 

 in the arkose, altho the surrounding magma may have contribu- 

 ted to their growth. One of the specimens showed, in a small 

 cavity, well terminated crystals of quartz, orthoclase, and horn- 

 blende, apparently outgrowths of these minerals in the arkose. 

 Calcite and datolite, which are found in some parts of the under- 

 lying arkose, are not found in this inclusion. 



The characteristics just mentioned show that this rock could 

 never have been fused. The retention of original cross-bedding 

 in another specimen^ is certain proof that the arkose could not 

 have flowed. 



Heated for thirty minutes at 1023°, this arkose showed no 

 trace of glass. The biotite and hornblende were destroyed, feld- 

 spars more clouded, magnetite and quartz unchanged. After sev- 

 enty-five minutes at 1150° the rock was more than half fused to 

 a bubbly glass of refractive index 1.490 to 1.502. The feldspars 

 were all fused, and only quartz and magnetite remained. Such 

 a rock containing unaltered feldspar might fuse at a somewhat 

 different temperature, but inasmuch as the feldspar was altered 

 in part before the intrusion of the diabase the temperatures here 

 observed are applicable. 



Fusion of underlying arkose and shale. As mentioned above, 

 we also obtained thru Professor Lewis specimens of the under- 

 lying arkose and shale at Granton, and it was upon these that 

 the preliminary fusion tests were made. It was only after sev- 

 eral measurements had been made on both rocks that datolite 

 (which does not occur •uniformly, and is sometimes entirely ab- 

 sent) was found in the arkose. Its presence renders the tests on 

 these rocks inconclusive, but the results are included as a matter 

 of record. 



Our specimen of the underlying arkose at Granton consisted 

 of about two-thirds alkali feldspars and nearly one-third quartz, 

 with some augite, the latter being in crystals partly inclosing felds- 

 par and quartz, as tho derived from constituents of the near-by 

 diabase and from chloritized biotite present in the arkose before 

 the intrusion. The feldspars had clear borders which had evi- 



^Lgc. cit., 1907, p. 135, (3). 



