H. H. Read—Contaminated Gabbro in Aberdeenshire. 181 
the great modification that the gabbro magma can undergo by the 
incorporation of sedimentary material. 
It may be useful to combine these observations into the following 
statement of mineral composition :— 
Hypersthene-gabbro : Labradorite, hypersthene, augite, 
magnetite. 
Contaminated gabbros: Labradorite, hypersthene, augite, 
magnetite, together with biotite, quartz, orthoclase, 
microcline, andesine, garnet, tourmaline, cordierite, 
sillimanite, spinel. 
RESULTS. FROM THE HuntLy Mass. 
The Huntly Mass! of younger igneous rocks is about 16 miles 
from north to south, with an average breadth of 3 miles in an east 
and west direction. At many localities in this large area, con- 
taminated gabbros are now known. Watt ? originally described them 
from Wells Cuternach. I have found them extremely well developed 
at the following independent localities : (1) near Ward ; (2) Battle- 
hill Quarry ; (3) Castle Bridge, Huntly ; (4) Hill of Kinnoir; (5) 
Rivestone ; (5) a great spread of about 1 square mile around Cuttle- 
hill ; (7) Fowlwood ; (8) Barry Hill ; (9) Wether Hill. The last three 
localities are in Banfishire. Most, but not all, of these localities are 
at the margin of the igneous mass. Here the contaminated gabbros 
form the matrix between lumps of partly digested hornfels ; the 
digestion may sometimes proceed so far that a fairly homogeneous 
contaminated gabbro results. 
Watt gave an excellent description of the Wells Cuternach rocks, 
together with an analysis in which it was shown that over 50 per 
cent of the rock was composed of cordierite. He distinguished two 
stages of contamination : first, the formation of cordierite-norites, 
and finally the formation of garnet-labradorite-biotite rock. 
The Cuternach locality presents several points of difficulty. The 
neighbouring igneous rock is a so-called picrite,? which may be taken 
to form the basal part of the composite intrusion of the Huntly Mass. 
Between the picrite and the schists to the west, appear the Cuternach 
cordierite-norites. Three views may be taken of these relative 
positions. 
(1) The basal picrite has been modified by the incorporation of 
sediment to produce cordierite-norite. 
(2) Or there was an original norite intruded between the picrite 
and the sediments to the west to provide the igneous magma for 
the contaminated norite. 
(3) Or the contamination of the original gabbro magma of the 
1 H. H. Read, Summary of Progress for 1918, 1919, pp. 28, 29. 
2 W. BR. Watt; loc. cit. 
3 W.R. Watt, loc. cit., p. 274. H. H. Read, Summary of Progress for 
1918, 1919, p. 28. 
