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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 Excerpt: ...However, it has been impossible to distinguish the diabase dikes of different ages, and they are described together. (See pp. 94-97.) It is possible that some are related to the subalkaline rocks, cutting them according to the normal sequence of eruption. So far as known all the dikes that are possibly related to the subalkaline rocks are normal diabase. They have been greatly altered and contain but little of the original augite, most of which has gone ever to hornblende. The plagioclase is saussuritized and is not determinable. As far as could be detected olivine is rare. Magnetite is, however, abundant. MAGMATIC RELATIONS. The rocks of the subalkaline group are almost certainly magmatically related and from their structural relations apparently make up one large batholith. Most of the rock of this batholith is gabbrodiorite, and it is one of the largest batholiths known of such a basic composition. The comagmatic origin of the subalkaline rocks is well shown by certain peculiarities which can be traced throughout the group. The rocks are all rich in ferrous iron, and the more salic are comparatively high in lime. In all of them soda exceeds potash. Titanium, occurring in ilmenite, titanitc, and 'rutile, is high. AU the rocks have undergone considerable contact and dynamic meta160145--21 i morphism and the granodiorites deep secular weathering. Epidote, zoisite, and some calcite are universal alteration products. The rocks are also transitional in part. On account of the faults that separate the various types and that bring contracted types in contact with each other no one continual section could be taken along which a gradual transition could be shown. It would be possible, however, to collect specimens--and this has been done by. the writer--which show...
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