W. M. Hntchings—Roclis of Great Whin Sill. 125 



AVhin Sill, 100 feet thick. Yeei thick 



No. 1. Limestone, with garnets, etc., where impure ; 

 white and sugary where pure, but containing 



patches of altered shaly matter, sandstone, etc. 24 



No. 2. Shale, weathered 12 



No. 3. Limestone ... ... ... ... ... ... 10 



No. 4. Shale, weathered ... ... ... ... ... 6 



No. 6. Limestone ... ... ... ... ... ... 2 



No. 6. Sandy shale 3 



No. 7. Limestone, hard blue, with fossils ... ... 8 



No. 8. Flaggy sandstone 10 



No. 9. Shale with nodules ... .,. ... 8 



No. 10. Basement conglomerate ... ., 2 



Total of sedimentary beds ... ... 85 



The specimens examined gave results as follows : — 

 No. 1. This limestone has been described above, so far as concerns 

 the garnet and idocrase-bearinghornfelsy alteration-product, of which 

 an analysis was also given. This analysis showed a large excess 

 of soda. But it was another hand-specimen from the same locality, 

 with both pure limestone and a layer of the hornfelsy material, 

 which gave the figures just quoted, showing potash in large excess 

 over soda. 



In this limestone-bed occur patches and lenticular masses of 

 altered sandstone and shale. A specimen of such a sandstone shows, 

 in the sections, that it is rather coarse-grained, with a good deal 

 of interstitial matter of originally argillaceous nature, with fine- 

 grained quartz. This matter is all intensely altered, showing some 

 newly-formed mosaic of quartz and a little felspar, a lot of white 

 mica in beautiful tufts and bunches, and here and there patches 

 of newly-crystallized, glassy-clear groups of well-twinned plagioclase 

 crystals, some of them identifiable as albite. The alkali-contents 

 of the rock are : — 



Potash ... ... ... ... ... ... 0'55 percent. 



Soda 2-71 ,, 



A patch of shale from the same source shows alteration on the 

 usual lines — much of the indefinite new " speck ly " product, vrhite 

 mica, chlorite, etc., with " spots " containing more chlorite, less 

 mica, and great aggregations of rutile grains. It contains : — 



Potash ... ... ... ... ... ... 4'82 percent. 



Soda 1-48 



No. 2. This was a moderately quartzy shale. The quartz is 

 not much affected, but the main mass is greatly altered, chiefly 

 to speckly matter and white mica, the latter often forming clear 

 patches and circular spots of larger, clearer flakes of muscovite, or 

 of muscovite and chlorite. The rock contains : — 



Potash ... ... ... ... ... ... 5'36 percent. 



Soda 2-93 ,, 



No. 3. Limestone, originally impure with argillaceous matter. 

 The bulk of it is not highly altered, not even i-endered coarsely 



