Ranges of Argillaceous Slate. 289 



Franklin County Argillaceous Slate. 



It will be seen by the map that this range occupies a considerable 

 part of the town of Bernardston, passing into quartz rock on the 

 east, and into mica slate on the west, and embracing a considerable 

 part of two mountains of considerable height. It is not, however, 

 till we pass into Vermont, that this slate assumes its most perfect 

 characters. In Bernardston it is quarried, indeed ; but not I believe 

 for roofing slate. But in Guilford, which adjoins Massachusetts, sev- 

 eral quarries are opened for this purpose. It there forms hills of 

 considerable elevation ; and such is its character farther north. It 

 has been traced northward, in the valley of the Connecticut, 80 or 90 

 miles, in Vermont ; nor do I know that its northern limit has yet 

 been ascertained. 



Berkshire County Argillaceous Slate. 



This ought perhaps rather to be called the argillaceous slate of 

 Renssalaer and Columbia counties : for the principal part of it lies 

 in New York, in the eastern part of these counties. Near the west- 

 ern line of Massachusetts it passes into mica slate, talco-argillaceous 

 slate, and chlorite slate, by taking mica, talc, and chlorite, more or 

 less abundantly, into its composition. The same rock forms hills 

 and patches of limited extent in Williamstown, New Ashford, Rich- 

 mond, West Stockbridge, Egremont, and Sheffield. But in no place 

 in Massachusetts will it answer for roofing slate. For this purpose 

 it is wrought extensively in Hoosac, Lebanon, and Hillsdale, N. Y. 

 I doubt very much whether the whole of this stratum in Massachu- 

 setts should not be regarded as an imperfect kind of mica slate, simi- 

 lar to an intermediate rock of doubtful character occurring in Haw- 

 ley, Plairifield, &c. which I have ranked with mica slate. Still, as 

 Professor Dewey, who has examined this rock more than I have, re- 

 gards it as argillaceous slate, I follow his judgment. 



On the west, this range is connected with the graywacke forma- 

 tion of Renssalaer and Columbia counties ; and on the east, it is as- 

 sociated with mica slate, and a limestone usually regarded as prim- 

 itive. 



Dip, Direction, and Thickness of the Strata. 



Excepting in the argillaceous slate connected with the graywacke, 

 I have not been able to find in this rock planes of stratification run- 

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