Prof. Dr. T. G. Bonne// — Troldolite, etc., in Aberdeenshire. 445 



scopically the only difference between this serpentine and that of 

 Belhelvie is that in the former there are much larger masses of 

 the bastite and much less of its steatitic alteration products. Under 

 the microscope the differences are but varietal, — rather less olivine 

 remains unchanged, and the slides have a rather greener hue ; this 

 colour here and there occurring rather markedly in little filmy 

 patches, as if a small amount of a chloritic mineral were present. 



Professor Heddle gives an analysis of this bastite, freed as far as 

 possible " from the dark serpentinous rods which penetrate the 

 mineral in so singular a manner " (these of course are the included 

 grains of serpentinized olivine). 



By the side of it (I.) I place for comparison an analysis (II.) of 

 the bastite from Baste ^ (Kohler, quoted by Dana, Mineralogy, p. 469) : 



I. II. 



Si02 38-186 43-90 



AI2O3 2-178 1-50 



CroOa -276 2-37 



FeaOg -028 



FeO 8-479 10-78 



MnO -513 -55 



CaO 2-912 2-70 



MgO 31-418 26-00 



KaO 1-401) .,„ 



Na^O 065| *' 



H2O 14-030 12-42 



100-486 100-69 



Enstatite, more or less altered, is common in British serpentines, 

 but this is the first instance I have seen of the varietal form bastite, 

 • — if we restrict this name to the large grains vpith inclusions of 

 more or less altered olivine. 



I pass on now to the rock of the Black Dog. This, according to 

 Professor Heddle, " consists of crystals of talc, matted in such con- 

 fusion as to form both a tough and a hard rock." As talc is about 

 the lowest mineral in the scale of hardness, and its allies steatite, 

 agalmatolite, etc., are all rather soft ; and as minerals do not 

 genei'ally change their physical characteristics, however confusedly 

 they may be matted, I looked forward to the examination of the 

 Black Dog with much interest. Wet as it was with waves and rain, 

 I could only see that it was a mottled dull-green to black rock, 

 sparsely speckled with small scales of a silvery mica, and not unlike 

 the troktolite ; when dry, however, it appeared slightly foliated in 

 structure. Smoothed by the action of the waves it presented 

 but few prominences. Selecting one of the least unhopeful I en- 

 deavoured to detach a specimen. A very few minutes sufficed to 

 show the impossibility of any form of talc being the dominant 

 mineral. I plied vigorously a fairly heavy hammer for about five 

 minutes, first at one place, then at another hard by it, with only this 

 result : — that I detached one chip about as large and as thick as 

 a florin and a number of tiny splinters. The latter had set their 



1 Comparison of these renders it highly prohable that II. was more completely 

 freed from the olivine grains than I. 



