The Accessory Minerals of the Granitic Rocks of theEnglish Lake District

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Abstract
I. Introduction. For some time past both of us have been engaged in investigating the mineral composition of certain sands and sandstones. These researches, although quite independent, were carried on in the same laboratory, and in both cases similar problems were encountered as to the derivation of certain minerals, notably those that frequently occur as accessories in igneous rocks. It was found desirable, therefore, to make a study of these minerals in their original habitat: for this purpose certain typical granites and other rocks were treated by the methods described in the following pages, and the accessory minerals were isolated for detailed study and comparison. The results obtained were so interesting, and in some instances so unexpected, that it was determined to make a joint study of the accessory minerals of some well-defined group of rocks. For various reasons, the granitic intrusions of the English Lake District seemed to offer a promising field. In nearly all instances abundant material was already available, collected at various times within the last twelve years, in the course of work already published and for various other purposes. The most important intrusions of the Lake District are, as is well known, the granites of Shap, Skiddaw, and Eskdale, and the Buttermere-Ennerdale granophyre. Most of these possess numerous apophyses, some acid, others more basic in character, as well as, in some instances, interesting variations within the mass of the rock. The intrusions generally known as the ‘microgranites’ or ‘felsites’ of Threlkeld and St. John's Vale, being

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