THE MANSFIELD SLATE. 55 



the Micliigamme dam, on the section hne between sees. 7 and 18, near the 

 southeastern and northeastern corners, respectively, the contact between 

 the three kinds of rock, the sedimentaries, the volcanics, and the intrusives. 

 Where the water leaves the eruptive and enters the sedimentary area the 

 more easily erodible nature of the rocks of the latter is well shown by the 

 falls which have been formed, the A'olcanics constituting the ban-ier over 

 which the water plunges into a deep basin worn from the slates. Crossing 

 the slates in the same direction, i. e., southeast, the river strikes squarely 

 against the intrusive dolerites and is deflected to the south, following the 

 contact between the two rocks for a short distance, then gradually working 

 to the west into the center of the sedimentary area, the river takes an 

 almost directly southerly course, with only minor bends. In the slates the 

 river has fairly low flat banks on both sides. In the southern jDortion of 

 the area the valley is narrower, owing to the progressive narrowing of the 

 sedimentary belt. As soon as the river leaves the Mansfield slate belt, 

 it resumes the sinuous course it had before the Mansfield belt is entered, 

 and flows between high banks tlu'ough the intrusives, out through the sand 

 plains near Lake Mary. 



POSSIBLE CONTINUATION OF THE MANSFIELD SLATE. 



In sec. 10, T. 44 N., R. 32 W., about 7 miles northwest of the extreme 

 northern end of the Mansfield area of slate, there are one or two exposures 

 of much crumpled interbedded brown and black slates. Their strike is about 

 N. 16°-20° W., but owing to their plicated condition the dip varies from 55° 

 southwest over to 85° northeast. The average dip, however, is presumed 

 to be to the southwest, which is in accord with the general structure of the 

 area. 



The slate exposures are surrounded by coarse-grained basic intrusives, 

 dolerites, which outcrop within short distances on all sides. The nearest 

 sedimentary beds are quartzose dolomite ledges which outcrop 1 J miles to 

 the east, in sees. 1 and 12, T. 44 N., R. 32 W., rather close to the Archean 

 granite. A section across the Lower Huronian rocks at this point shows 

 the Ai'chean granite overlain by quartzose dolomite, which is in its turn 

 overlain by the slates. The relations which these rocks bear to one another 

 are those wliich similar ones bear to one another near Micliigamme Moun- 



