394 sosMAN AND merwin: data on palisade diabase 



dently grown upon the original feldspar grains, partly filling the 

 pores of the rock with fresh feldspar. Calcite and datolite also 

 occurred as pore-filling minerals. 



Heated for fifteen minutes at 950°, the arkose showed no ex- 

 ternal change. A small amount of glass was found, formed by 

 the fusion of datolite. The quartz appeared unchanged. After 

 fifteen minutes at 1150°, glass was again present, resulting as 

 before from fusion of datolite. Seventy-five minutes at the same 

 temperature produced 10 to 15 per cent of glass of index 1.50- 

 1.52. The orthoclase had begun to fuse around the edges of 

 crystals and around the inclusions contained in the crystals. 



Our specimen of the underlying shale was a very fine grained 

 rock of density 2.59, banded with white and blue-black streaks, 

 and having coarser lenses containing garnet. In the white por- 

 tion quartz was identified, and probably andalusite. 



Heated for fifteen minutes at 950°, the finest grained parts of 

 the rock showed no marked change and no glass could be found. 

 Fifteen minutes at 1150° caused the fragment to flow, and sev- 

 enty-five minutes at the same temperature converted over one- 

 half of it into glass of refractive index 1.51 and less, with a few 

 fragments of original quartz remaining. But the extremely fine 

 grain of the rock rendered it unsatisfactory for these experiments. 



Both the shale and the arkose just described contained min- 

 erals of secondary origin resulting from the intrusion. Some of 

 these probably formed during the period of cooling; therefore 

 effects produced by heating these rocks might be quite different 

 from those which might have been caused at the same temperature 

 in the original rock. * 



Conclusion. The foregoing facts may be summarized in the 

 following statements: (1) The ''basaltic" facies of the Palisade 

 diabase begins to fuse at about 1150°, and enough of it is fused 

 at 1225° to permit the rock to flow; (2) The arkose now found 

 in the diabase in the form of inclusions is more than half fused at 

 1150°, but shows no fusion at 1025°. (3) These inclusions as act- 

 ually found show no indication of fusion or flow. 



As indicated by their present properties under atmospheric pres- 

 sure, there is therefore a gap of at least 100°, and probably more, 

 between the maximum temperature to which the arkose inclusions 



