found in the Neighbourhood of Glasgow. 409 



prism is commonly terminated by eight faces, constituting two 

 four-sided prisms of different inclinations. 



It contains about 16^ per cent, of soda, and 9^ per cent, of 

 water. The other constituents are silica and alumina. 



Its constitution is 3 Al S + N S 3 + 2 Aq. 



Mesolite. Natrolite in a pure state, that is perfectly 

 destitute of lime, is uncommon in this neighbourhood. Al- 

 most always we find a mixture of soda and lime constituting 

 the mesolite of Fuchs and Gehlen ; they gave it that name 

 because they considered it as intermediate between natrolite 

 and scolezite, or composed of an integrant particle of natro- 

 lite united to an integrant particle of scolezite. 



Mesolite is abundant both in this locality and in various 

 other parts of Scotland, where trap rocks occur; and we 

 find it in two different states. 



(1.) In four-sided prisms generally united so firmly to each 

 other, that we cannot easily separate them. Fine specimens 

 of this variety are found at present at Bishoptown in Renfrew- 

 shire, where a hill is perforating for a tunnel, constituting part 

 of the Greenock and Glasgow rail-road, at present forming. 

 This variety approaches very nearly to natrolite ; since it 

 contains only 1^ per cent, of lime, while there is no less than 

 13 per cent, of soda, and a small portion of potash. If na- 

 trolite be 



SA1S + NS 3 + 2Aq, 

 this variety will be 



3 Al S + (f N + &K + & Cal) S 3 + 2 Aq. 



Its specific gravity is 2'1365. 



The other variety constitutes veins in the rock. It is much 

 softer, has a foliated texture, and a specific gravity of 2'212. 



It contains 6^ per cent, of soda and 3 per cent, of lime; 

 so that the atoms of soda are very nearly twice as numerous 

 as those of lime. In other respects its constitution agrees 

 nearly with the other variety. 



4. Scolezite. This is the mineral which Werner distin- 

 guished by the name of needle zeolite. It occurs often in 

 long needles, as fine as human hair, and quite flexible ; some- 

 times in needles of a longer and larger size, and irregularly 

 interlaced ; sometimes the needles are firmly attached to each 

 other, so as to give it a splintery appearance. In this state it 

 is harder than calcareous spar ; whereas the hairy variety 

 is quite soft. In some specimens the central portion is hard 

 and splintery, while the outer portion is quite soft and friable. 

 We would naturally suppose that this friability was owing 

 to the loss of a portion of water ; but on examining some re- 



