178 H. H. Read—Contaminated Gabbro in Aberdeenshire. 
is cordierite-norite, but other mixed rock types, of unquestionably 
similar origin, occur very abundantly in Aberdeenshire and the 
general group name of Contaminated Gabbro has been provisionally | 
adopted for rocks resulting from a gabbro magma contaminated 
with sedimentary material. 
Before 1914 two occurrences of contaminated gabbro had been 
described, one in France, the other in Minnesota. In 1898-9 an 
account of the cordierite-norites of Le Pallet, Loire-Inférieure, was 
given by Lacroix. In 1900 A. N. Winchell * published the results 
of a very detailed mineralogical and petrographic study of cordierite- 
norite, quartz-gabbro, and orthoclase-gabbro from Minnesota. Both 
authors held admixture with sedimentary material to be the cause 
of these modifications of the normal gabbro magma. 
In 1914 W. R. Watt ® described cordierite-norites and associated 
rocks from Wells Cuternach, near the farm of Drumdelgie, 3 miles 
west-north-west of Huntly, Aberdeenshire. He said :— 
“Tt appears certain that the rocks of this (Cuternach) type 
originated from a magma contaminated by the aluminous material 
of the phyllites. 
“ Tt is greatly to be regretted that no clear sections exist to prove 
in the Huntly occurrence a gradual transition from undoubted 
igneous rock to undoubted phyllite ” (loc. cit. p. 288). 
In 1919 the localities of this type of cordierite-norite were vastly 
increased, contaminated norites being shown to occur over great 
parts of the Huntly Mass." Moreover, sections were discovered which 
showed that there could be no doubt that the formation of cordierite- 
norites and allied contaminated rocks was due to the incorporation 
of sedimentary material in the gabbro magma. 
A year later the distribution of contaminated gabbros was again 
widened by their discovery as a marginal modification of the 
hypersthene-gabbro of the independent Insch Mass near the farm of 
Easter Saphook, 24 miles west by north of Old Meldrum.’ During 
this year (1920) im an investigation of the igneous rocks of the 
Arnage Mass, undertaken during leave from official work, I have 
found that contaminated norites bulk very much larger than the 
uncontaminated nuclear norite. It may be said, then, that con- 
taminated gabbros occur, so far as is known at present, in the Huntly, 
Insch, and Arnage Masses, and there is every possibility that their 
distribution will be still greater as the remaining younger igneous 
masses of North-East Scotland come to be studied. 
1 A. Lacroix, ‘‘ Le Gabbro du Pallet et Ses Modifications’’: Bull. Carte 
Geol. de la France, vol. x, 1898-9, pp. 341-96. 
2 A.N. Winchell, ‘‘ Mineralogical and Petrographie Study of the Gabbroid 
Rocks of Minnesota, etc.’? : American Geologist, vol. xxvi, 1900, p. 294 et seq. 
3 W. R. Watt, ‘‘Geology of Country around Huntly (Aberdeenshire) ”’ : 
Q.J.G.S:, vol. lxx, 1914, pp. 266-93. 
4H. H. Read, Summary of Progress for 1918, 1919, pp. 29, 30. 
° H. H. Read, Summary of Progress for 1919, 1920, p. 26. 
