126 GEEEN MOUNTAINS IN MASSACHUSETTS. 



tion foliation is no longer visible IA*. A .secondary cleavage, resembling a minute 

 jointing, occurs in scattered localities. V. The degree and direction of the pitch of a 

 fold are often indicated by those of tlie axes of the minor plications on its sides. VI. 

 The strikes of the stratification foliation and cleavage foliation often differ in the same 

 rock, and arc then regarded as indicating a pitching fold. VII. Such a correspondence 

 exists between the stratification and cleavage foliations of the great folds and those 

 of the minute plications that a very small specimen properly oriented gives, in many 

 cases, the key to the structure over a large portion of the side of a fold. 



On these principles twelve complete and three partial transverse sections have 

 been constructed across the Greylock mass (Pis. xvm-xxii). .These show that the 

 range consists of a series of more or less open or compressed synclines and anticlines, 

 which, beginning near North Adams, increase southerly in number and altitude with 

 the increasing width and altitude of the schist area, and then, from a point about a 

 mile and a half south of the summit, begin to widen out, and to diminish in number 

 and height until they finally pass into a few broad and low undulations west of 

 Cheshire. Between that point and the villages of Berkshire and Lanesboro the folds 

 become sharper and more compressed, and the schist area rapidly narrows, termi- 

 nating within a short distance of Pittsfield. The two most comprehensive and best 

 substantiated of these sections (G and I) begin near South Adams, cross the central 

 ridge north and south of the summit, then follow the two great western spurs, and 

 end near South Williamstown. The sections are described on p. 100, the first two in 

 some detail. The section lines on the map (PI. i) and the epitomized sections in Fig. 

 72 on p. 17S show the relations of the fifteen sections to each other. 



Resume, structural. — Mount Greylock with its subordinate ridges is a synclinorium 

 consisting in its broadest portion of ten or eleven synclines alternating with as many 

 anticlines. While the number of these minor synclines is so considerable at the sur- 

 face, in carrying the sections downward they resolve themselves chiefly into two 

 great synclines with several lateral and minor ones. The larger of these two forms 

 the central ridge of the mass; the smaller one, east of it, forms Kagged mountain and 

 an inner line of foot-hills farther south. The anticline between these coincides with 

 the Bellowspipe notch; that on the west of the central syncline is on the west side 

 of the north south part of the Hopper. The major and central syncline is so com- 

 pressed east of Syniouds peak (Mount Prospect) and Bald mountain, and its axial 

 plane is so inclined to the east that the calcareous strata which underlie the central 

 ridge have on its west side a westerly dip. Farther south this syncline opens out, 

 and all the relations become more normal. On either side of those two main synclines 

 the subordinate folds are more or less open and have their axial planes vertical or inclined 

 cast or west. The long undulations in the axes of these synclines are shown in four 

 longitudinal sections (PI. xxm): Section 1', tin- eastern or Kagged mountain syncline; 

 0, the central or Greylock syncline, and E' K". portions of two of the minor synclines 

 on the west flank of the mass, In each of the sections P and CJ the trough bottom 



