€feology, ^c. ef the Connecticut. 35 



9. Argillite. 



Colored Brick Red. 



The remarks last made in regard to the primitive green- 

 stone, chlorite slate, &c. will apply to this rock. Fof we find 

 it near the two terminations of the secondary tract and on the 

 same side of it — viz. in Woodbridge at the south end, and com- 

 mencing on the north at Leyden and extending at least as 

 far as Rockingham, Vermont. The northern deposite is 

 much the most extensive and is best characterized. In both 

 places, however, it is often tortuous and slightly undulating, 

 especially when passing into mica slate. It embraces nu- 

 merous beds and "tuberculous masses" of white quartz — 

 perhaps the milky quartz. The passage into mica slate is 

 usually very gradual, the characters of the argillite losing 

 themselves by imperceptible changes in those of the 

 mica slate, so that for a considerable distance, the observer 

 may be in doubt to which rock to refer the aggregate. The 

 Woodbridge argillite occasionally alternates with mica slate, 

 (Journal Sci. Vol. 2. p. 203.) and I have ascertained that 

 this is the case also with that of Vermont. That which is 

 just beginning to pass into mica slate, alternates also with a 

 peculiar coarse limestone to be described under the next ar- 

 ticle ; or rather, the limestone forms beds in the argillite — 

 for instance in Putney. 



A principal object in extending the map so much beyond 

 the secondary region on the north, was to include all the 

 argillite to be found along the Conneeticut. Whether I have 

 effected this object I am not certain. The Rev. E. D. 

 Andrews, who communicated to me several facts on this 

 subject, is of opinion that the northern limit of the argillite 

 is on the south side of Williams' river in Rockingham, three 

 miles north of Bellows Falls; but he had not examined the 

 regions beyond with sufficient care to decide the point with 

 certainty. 



In Guilford, Vermont, this argillite alternates with a pecu- 

 liar rock which Professor Dewey remarks appears " to be 

 a talco-argillite with much quartz." Its stratification is less 

 perfect than the argillite ; or, rather, it has more of the ir- 

 regularities and tortuosities of mica slate. Its small extent 



