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The axis of a well-marked anticlinal extends from the south- 

 west end of the Concord and Westborough peninsula of 

 Huronian beds through Grafton, Milbury, Sutton, and the 

 western part of Douglass to and along the western border of 

 Rhode Island. West of this somewhat curving axial line the 

 gneiss dips to the W. and W.N.W. at angles varying from 

 25° to 75°, passing beneath the Worcester and Webster belt 

 of mica slate, which lies in a closed synclinal. On the east 

 the prevailing dips are to the E. and E.N.E. ; and the anti- 

 clinal is less steep in this direction, the inclination of the strata 

 falling, usually, between 25° and 50°. Crossing this eroded 

 anticline from the crest eastward, we pass, of course, as on the 

 west, from older to newer rocks. Beginning in Douglass, for 

 instance, with the coarse, granitic, frequently but little mica- 

 ceous and often apparently unstratified gneiss, which forms the 

 base of our Montalban, we pass up gradually, in Uxbridge, to 

 gneiss which is more micaceous, and distinctly stratified in thin 

 beds, with now and then a layer of true mica slate. While 

 still higher, in Blackstone, we find fissile gneisses, rich in mica, 

 alternating with and gradually giving place to mica slate and 

 quartzite ; mica slate being the prevailing rock in the eastern 

 half of this town. Although this Blackstone mica slate is less 

 easily separable from the underlying gneiss than the great mica 

 slate formation of the Merrimac, Nashua, and Blackstone 

 Valleys, so much so that it can hardly be mapped as a distinct 

 lithologic belt, yet I am obliged to regard it as occupying 

 essentially the same horizon, and as being, in a general way at 

 least, the stratigraphic equivalent of the mica slate on the west 

 side of the anticlinal, in Webster and Oxford. 



The mica slate seems to pass gradually upward into and to 

 be continuous with the " metamorphic slate," which begins in 

 the eastern part of Blackstone, near Mill River, and extends 

 into the western edge of Franklin, showing at most points E. 

 or E.N.E. dips of 20° to 40°, and having a breadth of about 

 three miles. On the line of the New York and New England 

 Railroad it is met abruptly on the east by coarse, granitoid 



