552 



Scientific Geology. 



and south than to east and west. The medium dip is from 60° to 70° 

 northwest. In the Worcester mica slate, the dip and direction are 

 much more irregular : though for the most part its strata run nearly 

 northeast and southwest and dip northwest at a large angle. But to- 

 wards the southern part of the range, they run nearly north and south; 

 and towards the northeast part of the range, they run nearly east and 

 west, conforming apparently to the curve which the western margin 

 of the gneiss forms. The western part of this mica slate range ap- 

 pears to belong to theoldest meridional system that has been described. 

 As to the argillaceous slate, contained in this formation, I suspect that al- 

 so to be connected with the same meridional system : though I have not 

 observed its dip and direction in places enough to enable me to forma 

 very confident opinion on this point. 



I am strongly suspicious, that the mica slate of Worcester Valley, 

 will be found to be not perfectly conformable in its stratification to the 

 gneiss on either side of the valley ; in other words, that the gneiss 

 was partially elevated previous to the deposition of the mica slate. 

 If so, that epoch of first elevation is probably the oldest in Massachu- 

 setts. But there is so much of irregularity in the dip of this rock, 

 that I do not presume to erect another system upon so uncertain a 

 foundation. 



An inspection of Plate XV, will show clearly that the graywacke 

 formation belongs to two very distinct systems of elevation: the one 

 running nearly east and west, and the other not far from northeast 

 and southwest. A tract of some width, extending from Walpole to 

 Providence, and indeed to Newport, belongs to the latter system; al- 

 though on the island of Rhode Island, there is not a little irregularity 

 in the dip and direction. Obviously this part of the graywacke be- 

 longs to the northeast and southwest system under consideration. 

 The talco-chloritic slate in Cumberland and Smithfield, also, as well 

 as a part of the mica slate connected with it, appear to belong to the 

 same system ; and since the prevailing dip is southeasterly, (although 

 in this there is great irregularity,) it would seem that there may be 

 an anticlinal line between the graywacke and the gneiss east of Wor- 

 cester which dips in a contrary direction. 



Along the western margin of the tongue of graywacke extending to- 

 wards Sherburne, the direction of the strata corresponds with this 

 system I for example in Natick and Watertown : and probably is to 

 be reckoned as a part of it. 



The tendency to a northeast and southwest direction, which 1 have 



