732 THE JOURNAL OF GEOLOGY. 



quently induced cleavage structure. In this particular the prob- 

 lems 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 excep- 

 tion 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 topo- 

 graphical 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 con- 

 structed. 



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 suffi- 

 cient to entirely counteract the very considerable northerly pitch 

 of the southern portions of the mass. 



Structure of the Mountain. — The sections show that the south- 

 ern portion of the mountain is a geo-anticlinal in the Riga 

 Schist, probably with moderate minor folds tolerably symme- 

 trical. Within the core of this anticlinal is the Canaan Dolomite', 

 which appears from under the schist to the southeast of the 



1 An extensive study of the subject of secondary cleavage as it is met with in the 

 Greylock area, has been made by M'r. T. Nelson Dale, and will appear in full in a 

 monograph by Professor Pumpelly on the Geology of the Green Mountains. A sum- 

 mary 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. 



