Dr. Heddle and Mr. R. P. Greg on British Pectolites. 249 



dently also pectolite ; it is included in mineralogical works under 

 the head of table spar, but containing soda, it must be pectolite, 

 which differs from table spar merely in silicate of soda replacing 

 silicate of lime. Walker's mineral then in all probability is 

 identical with the mineral discovered by Lord Greenock ; we are 

 not, however, aware that it has been lately found at this place. 



Again, Thomson describes among the zeolites a mineral to 

 which he has given the name of " stellite," found in greenstone 

 at Kilsyth ; the original specimen analysed by Dr. Thomson we 

 have lately seen, and do not hesitate in saying it is ordinary pec- 

 tolite, as indeed its analysis (made by Dr. Thomson evidently on 

 an impure portion) had before led us to suppose. 



Mr. Rose of Edinburgh states, that Lord Greenock obtained 

 at Loch End a weathered specimen of this mineral, but we have 

 no analysis of this specimen. 



Then we have the so-called " Wollastonite " of the Castle 

 Rock of Edinburgh*, the analysis of which, according to Ken- 

 nedy, is given as No. 4 in the Table. 



Dr. Thomson sets aside this analysis, and states that the Wol- 

 lastonite of the Edinburgh mineralogists is prehnite. White 

 prehnite does occur along with the Castle Rock mineral, and as 

 our analysis agrees with the ordinary ones of pectolite, the con- 

 clusion is that Thomson's specimen contained prehnite, but none 

 of the substance in question. 



Our analyses, made on 25 grains, afforded, — 



a. b. 



Silica .... 55-12 53-06 



Alumina ... -30 46 



Oxide of iron . . -52 

 Lime . . .' . 3336 33-48 



Soda .... 7-85 \ 9-981 



Potash .... -36 J -29 J 



Water .... 3-13 not det. 



The second specimen was evidently the purest. 



Next we have to notice the specimens found by Mr. Forrest 

 in greenstone at Ratho, near Edinburgh. Here it occurs of a 

 pale green colour, and in orbicular masses with a fibrous and 

 radiating structure, at a depth of 90 feet, associated with stea- 

 tite, calcite, heavy spar, specular iron; also in pseudomorphs 

 after analcime, although analcime has not itself yet been found ; 

 and is found (though rarely) in distinct crystals. The fibrous 

 variety is extremely tough when first obtained, but soon weathers, 

 becoming asbestus-like on exposure. 



* Occurring in orbicular masses in trap, translucent and highly crystal- 

 line, with a radiating structure. 



