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THE JOURNAL OF GEOLOGY.

quently induced cleavage structure. In this particular the problems have been essentially those which were encountered in the Greylock area, and similar criteria have been made use of to distinguish the planes of stratification.^[1] Hence with the exception of those localities where contacts of the different rocks are exposed, dip observations have been possible at only a few localities where definite plications could be made out.

In the absence of dip observations, the sequence being known, many structural facts have been deduced from the areal relations of the several horizons. Next in importance as a method of determining structure is the interpretation of topographical features. It is by application of all of these methods, whose relative importance is expressed by the order in which they have been mentioned, that the sections have been constructed.

The longitudinal section (Fig. 3) which passes through the mountain in a general north and south direction, nearly at right angles to the cross sections just described, is constructed to show how the northerly pitch of the southern portion of the mountain carries the Canaan Dolomite and the Riga Schist so low that they do not appear again to the northward, for although the pitch in the northern part of the area is southerly, it is not sufficient to entirely counteract the very considerable northerly pitch of the southern portions of the mass.

Structure of the Mountain.—The sections show that the southern portion of the mountain is a geo-anticlinal in the Riga Schist, probably with moderate minor folds tolerably symmetrical. Within the core of this anticlinal is the Canaan Dolomite, which appears from under the schist to the southeast of the

↑ An extensive study of the subject of secondary cleavage as it is met with in the Greylock area, has been made by Mr. T. Nelson Dale, and will appear in full in a monograph by Professor Pumpelly on the Geology of the Green Mountains. A summary of his observations and conclusions is contained in the American Geologist for July, 1891. Mr. Dale has also published a paper entitled, "On Plicated Cleavage-Foliation," in the American Journal of Science for April, 1892. As the writer assisted Mr. Dale during a portion of the field investigation, he became familiar with the structures there exhibited, as he did later also in independent work in the northern stretch of the Taconic Range west of Williamstown.

[1] An extensive study of the subject of secondary cleavage as it is met with in the Greylock area, has been made by Mr. T. Nelson Dale, and will appear in full in a monograph by Professor Pumpelly on the Geology of the Green Mountains. A summary of his observations and conclusions is contained in the American Geologist for July, 1891. Mr. Dale has also published a paper entitled, "On Plicated Cleavage-Foliation," in the American Journal of Science for April, 1892. As the writer assisted Mr. Dale during a portion of the field investigation, he became familiar with the structures there exhibited, as he did later also in independent work in the northern stretch of the Taconic Range west of Williamstown.

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