the Silurian and Cambrian Limestones. 369 



6. Cambrian. — Limestone from Craigmuir near Inverary. 

 Metamorphic and not fossiliferous ; specimen from a series of 

 alternating beds of from 6 inches to several feet thickness of 

 limestone with clay-shales, and resting upon clay-slates. They 

 have an E. and W. strike, with dip of 30° to N., and are continuous 

 for many miles. 



This limestone is beautifully foliated by plates of silvery mica, 

 which separates in large quantities when the limestone is dis- 

 solved in acids. The foliation appears to be perfectly parallel to 

 the plane of bedding of the rocks. 



The limestone is compact, but not liard, and is of a grayish 

 colour, splitting easily along the planes of foliation, and the sur- 

 faces thus exposed being covered by a beautiful white mica. 



The specific gravity was found to be 2-73 at 60'' F. 29-23 

 grs. were analysed and yielded 9-41 carbonic acid, 7-08 insoluble, 

 residue chieily mica, 0-06 organic matter, 0-47 sesquioxide of iron 

 and alumina, 0-20 gr. phosphate of magnesia from the phosphoric 

 acid, and 0-05 ditto from the magnesia determination. 



These results afford the following per-centage composition : — 



Carbonate of lime 73-34 



Carbonate of magnesia. . . . 0*28 

 Sesquioxide of iron and alumina. 1-16 



Phosphoric acid 0-44 



Organic matter 0-21 



Insoluble 24-03 



99-46 

 Water and loss 0-54 



10000 



7. White limestone forming veins and irregular masses in the 

 hornblende schist at Kragerod, Norway, and having a peculiar 

 shell-like laminar structure. 



The hornblende schist in which this limestone occurs contains 

 numerous veins of phosphate of lime ; and this limestone was 

 analysed under the supposition, that, as it had apparently been 

 formed by the deposition from water filtering through the sur- 

 rounding strata, it would contain a large amount of phosphoric 

 acid, which, however, was not found to be the case. The specific 

 gravity was found to be 2-69 at 60° F. 



On analysis, 46-94 grs. yielded 4-24 insoluble, 0-36 organic 

 matter, 0-13 alumina, with phosphoric acid and trace of iron, 

 41-89 carbonate of lime, 0-07 oxide of manganese, and 0-16 gr. 

 phosphate of magnesia from the phosphoric acid determination. 



54-73 grs. examined for magnesia afforded 0-14 gr. phosphate 

 of magnesia, and 50-17 grs., dried at 300° F., yielded 0*11 

 water as loss. 



Fhil. Mag, S. 4. Vol. 13. No. 87. May 1857. 2 C 



