H. H. Read—Oontaminated Gabbro un pondieenenire! 183 
sediments. He also discussed the formation of quartz-gabbro 
and orthoclase-gabbro and concluded (loc. cit. p. 365) that the 
following modifications of the eabbro magma by sedimentary con- 
tamination had taken place :— 
(1) Digestion of aluminous sediment : cordierite-norite. 
(2) Digestion of siliceous schists or quartzite : quartz-gabbro. 
(3) Digestion of potassic rock : orthoclase-gabbro. 
From the field relations and mineral composition it is apparent 
that the contaminated gabbros of Huntly and Saphook are of 
similar origin to those of Le Pallet and Minnesota. The following 
tabular statement exemplifies the close resemblance between the 
four occurrences :— 
Saphook. Huntly. Le Pallet. Minnesota. 
Labradorite. Labradorite. = Labradorite. 
eae: Andesine. Acid andesine. Andesine (rare). 
Orthoclase. Orthoclase. a — 
Microcline. — — — 
Hypersthene. Hypersthene. Hypersthene. Bronzite-enstatite 
Biotite. Biotite. Biotite. — 
{ Cordierite Cordierite Cordierite Cordierite 
\ with haloes. with haloes. with haloes. without haloes. 
Garnet. Garnet. Almandine. No garnet. 
Quartz. Quartz. Quartz. Quartz. 
— — Staurolite ? Staurolite. 
— — Graphite. Graphite. 
Spinel rare. Spinel common. Spinel common. Spinel rare. 
Sillimanite. Sillimanite. Sillimanite. No sillimanite. 
CoNCLUSIONS. 
In North-East Scotland there is a great development of gabbros 
contaminated with sedimentary material. By the incorporation of 
this sedimentary material in the gabbro magma rocks are produced 
in. general of abnormal composition and characterized by minerals 
not proper to gabbro and often not proper to any purely igneous 
rocks. Sometimes, however, there may be produced a rock of 
undoubted assimilation origin, but which in mineral content 
approaches a purely igneous rock, though not a gabbro. The 
further exploration of the contaminated igneous rocks of North-east 
Scotland may, therefore, perhaps throw some light upon current 
theories of differentiation. 
