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. 1911 Excerpt: ... determined from the present investigations, are shown on PI. VIII (pocket), which gives the area and distribution of the anthracite, ...Read MoreThis 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. 1911 Excerpt: ... determined from the present investigations, are shown on PI. VIII (pocket), which gives the area and distribution of the anthracite, semianthracite, and semibituminous. Those limits are subject to revision in the light of further knowledge, especially where the lines are drawn through regions from which no samples have been tested. It will doubtless be found that such lines, as far as definite lines of separation exist, are sinuous, and that the area of each group contains outlying areas of the other groups. Within each of the groups as outlined above no regular variation has been noted. The explanation of this geographic variation is to be found in the relation to the structure. The anthracite occurs in a region of great structural complexity (p. 332), the rocks being very closely folded and much faulted. The coking coal occurs in a region of simpler structure in which the folds are open. The semianthracite occupies a region of intermediate structural type. Distance from the Chugach Mountains also doubtless has played a part in the distribution of the various kinds of coal, especially if there have been intrusions of large and numerous igneous masses subsequent to the deposition of the coal. Local intrusions are more abundant in the anthracite region, but appear not to be either numerous enough or large enough to have been primarily responsible for the regional variation in the coal. Where such dikes or sills (pp. 360-362) have come into direct contact with the coal they have driven off the volatile constituents and transformed part of it into a dense natural coke, as shown on PI. IX, B. The effect of such intrusion, as far as could be judged from the instances noted, was extremely local, the coal being altered for only a few inches from the contact COMPA...Read Less
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