Chemical Anal^es qf Hochn. .3SY 



coal formation, and in the body of the greenstone itself there 

 are numerous fragments of those rocks, esj^cially of the slate- 

 clay. The slate-clay, upon which the greenstone rests, and the 

 fragments of that rock contained in the greenstone, is so much 

 changed as to resemble some varieties of compact felspar. I 

 gave Mr Walker a specimen of slate-clay, taken from a bed at 

 a distance from the greenstone, and another from the upper part 

 of a bed of the same rock, in immediate contact with the green- 

 stone, with the view of being analyzed. The following re- 

 sults were obtained : 



1. Unaltered slate-clay from Lochend. Heated per se before 

 the blowpipe, it fuses with difficulty: with ammoniacal phosphate 

 of soda, it forms a white enamel ; with phosphate of soda, an ena- 

 mel yellowish-green when hot, and yellowish when cold ; with bo- 

 rax it forms a greenish glass. Its constituents are : Silica, 58.22 ; 

 Alumina, 17.50; Protoxide of Iron, 10.53; Lime, trace; Mag- 

 nesia, 4.62 ; Soda, 2.02; Water, 6.70; =: 99-59. 



2. Altered slate-clay from Lochend. This specimen, which 

 very much resembled some varieties of compact felspar, afforded 

 the following constituent parts: Silica, 53.25 ; Alumina, 17.56; 

 Oxide of Iron, 8.64 ; Lime, 6.62 ; Magnesia, 2.70 ; Soda, 7.85 ; 

 Water, 2.23 ; = 98.85. This analysis shews that the altered 

 slate has received a notable quantity of lime and alkali, thus 

 giving it a composition different from that of the unaltered va- 

 riety. 



Understanding, from the communication of a chemist, that 

 common alluvial clays contain alkali, I directed my young 

 friend's attention to this point, and he ascertained, as stated 

 above, that the unaltered slate-clay also contains alkali. The 

 importance of this fact as connected with soils is too evident to 

 require any particular consideration. 



Altered or Changed Slate^ Clay from a mass imbedded in the Green- 

 stone of Salisbury Craigs. 



Specific Gravity ^.52. Chemical Characters : Effervesces, and 

 does not gelatinise with acids. Before the blowpipe, heated per 

 se^ it melts into a transparent greenish glass ; witli salt of phos- 

 phorus into a transparent and colourless glass. Constituent 

 Parts: Sijica, 66.100; Alumina, 19-5 ; Oxide of Iron, trace; 



