Page:The Journal of geology (IA journalofgeology21894univers).pdf/437

age is produced. A beautiful example of this is seen in Fig. 1, from the schist phase of the conglomerate gneiss two miles north-east of East Clarendon, near its contact with a coarse underlying gneiss. Blue Ridge and Pico Mountains are now capped by schist produced upon the back of folds. Close folding with axes striking nearly north and south only occurs in the amphitheatre near the summit of the greatest elevations, as on Mount Holly—a hill about a mile south of the station by that name—and near the contact with the Mendon series. The rocks of the core have no persistent strike and dip, neither of schistosity nor bedding; east and west strikes are as numerous as those trending north and south and the dips are as variable. Throughout the core the gnarled and tortuous folding of the strata represents the effect produced by the operation of repeated periods of mountain-building action of enormous force, directed not always from the east and west as in the Mendon series, but from the north and south as well.

A careful study of the Mendon series recognizes but two periods of orographic disturbance, the second acting along approximately the same lines as the first. This is well-indicated under the microscope, and in the field it is beautifully shown at North Sherburne where the strike of the rock (a conglomerate) is N. 25° W.—a trend produced by the first period of folding. The schistosity of the Green Mountains traverses this obliquely, making an angle of 35°-40°, striking N. 10° to 15° E. Both structures dip easterly at a variable angle. Forces that induced the regional lamination of the range could not have produced the great variety of trend observed in the folding of the Mount Holly series. The question of difference of environment of the central or lower parts of anticlines as compared with the outer must not be overlooked. All the phenomena go to show that the superior or Mendon series was above the neutral zone and that great slipping, stretching and crumpling took place therein dependent upon position in this belt. Below the neutral zone during the folding of the Mendon series undoubtedly most of the core rocks were placed where crushing would largely