496 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
















which is now under the influence of wave action, has suffered no change | 
whatever. 
24. Though not immediately connected with augitic change, yet as bearing | 
on the origin of serpentine as a whole, I here insert the analysis of the yellow- 
green matrix in which these black pseudomorphs of augite were imbedded,— | 
the matrix which here represents the original labradorite-paste of the gabbro. | 
Specific gravity, 2° 616. | 
Silica, : ; : . 38°834 
Ferric Oxide, . : 2 O02 
Ferrous Oxide, . 5 ee O26 
Manganous Oxide, . : 167 
Lime, ; 3 ; , Tubroye 
Magnesia, . ; : . 38°756 
Water, . ; ; eenlib eons 
100+ 06 
So that the felspar here has been converted into a fully more typical serpentine 
than that which resulted from the change of the augite. This cannot be regarded 
as a common occurrence ; the felspathic constituent of the altered rock usually 
forming a substance more or less allied to kaolin. | 
It is, moreover, anomalous in another respect. As will be afterwards shown, 
the serpentinous change induced in the augitic mineral is generally effected | 
not by the direct introduction of magnesia, but by the abstraction of portions | 
of the other ingredients, and the resultant proportional increase of the non- 
abstracted magnesia. But here a direct insertion is requisite for the transmu- 
tation of the non-magnesian felspar, or at least an interchange between mag- 
nesia and certain constituents of the felspar. This will be after considered. | 
25. My next illustration of the same mode of change was got by Professor 
Nico, Mr DupGeon, and myself on the north slope of the Green Hill of Strathdon, 
in Aberdeenshire. It occurred in one of the bare spots on that grass-clad hill, | 
near the summit, in pieces about half the size of the hand ; they were somewhat 
loosely bedded. These pieces were of a dull olive-green colour passing to brown; 
they were of a laminated or flatly cleavable structure, much resembling that of} 
malacolite or sahlite. Between the cleavages there are reticulating crystals of} 
extreme tenuity, apparently of talc, possibly, however, of Brucite. This gives) 
the stone a false glimmering lustre resembling that of enstatite, while in reality) 
it is lustreless, somewhat porous, and resembles a close-grained gingerbread. 
It is soft and easily crushed. F 
The specific gravity is 1°753 when dry,—2 ‘158 after soaking for five hours] © 
in water. 
