Summary and conclusions

The nodules examined have been shown to contain a variety of minerals and to exhibit certain mineralogical and structural differences from one another or within the nodules themselves. The mineralogical differences serve to separate five definite types of mineral facies. There are also described types transitional between the nodules themselves, and between them and the surrounding rock, grading from types sufficiently aluminous to exclude the formation of wollastonite to less aluminous types in which this mineral is formed.

Owing to insufficiently prolonged variations of the metamorphic conditions equilibrium has not been established, and a remarkable series of replacement structures has been left in the rock by means of which the course of several stages of its metamorphism has been established.

Lack of knowledge concerning the metamorphic conditions previous to changes due to the influence of the surrounding diorite, the isolated character of the nodules and the intricacy of the relationships between the minerals render the origin and metamorphism of these nodules subject to a variety of interpretations. The balance of evidence seems in favour of the one put forward here.