93 TACOHIC SYSTEM IN RHODE-ISLAND. 



still preserves the general character of the Magnesian Blate, and is a perfect example of it 

 throughout most of its bodj . 

 There still remained other members of the Taconic system, which I had not yetdis- 



. u-il in this narrow basin or trough. As the granite appeared in a heavy body upon 

 the woi of the slates and limestones, 1 pursued an easterly route for the discover] of other 

 members of the system. 1 was ltd upon this direction, too, from having seen boulders of 

 brown Bandstone in the drill of the Blackstone valley, which increased in size and num- 

 bers towards the river. Pursuing, therefore, this direction, I soon came upon an extensive 

 deposit of this rock in place about half a mile north of the Cumberland coal-field. On 

 the direct unite from Smithfield to Cumberland, the quartz, if it exists, is concealed beneath 

 thick beds of drift. The quartz is upon the eastern side of the Blackstone. As developed 

 in this valley, it is a line brown granular quartz, interlaminated with slate, or rather alter- 

 nating with a Bpecies of magnesian Blate, but of a darker color and more siliceous than this 

 rock usually is. Tin lower mass of quartz is about fifty feet thick : it is then succeeded 

 by ten feet of slate, about five of quartz, and then about seventy-live of slate, which, how- 

 ever, is very siliceous, and interlaminated with sortie beds of quartz. Without entering 

 upon minute details of the alternations of these masses, 1 estimated the whole thickness 

 at live hundred feel. The quartz trends N. 35° E. ; its angle of dip about 35°. Near Mr. 

 Whipple's tavern, the trend is N. 10° W. ; dip, 80° E. At half a mile north of Whip- 

 ple's, the trend is N. 55 D E. A fracture traverses this rock in the direction of N. 15° W., 

 in which direction there are low ranges of rounded hills. 



Having traversed the Blate, limestone and quartz, on a route which is nearly perpen- 

 dicular to their strike, 1 had reason to believe that the remaining members of the Taconic 

 -in. which I was familiar within New-York and Massachusetts, were wanting here. 

 I mad.' do farther examinations than those I have already detailed, having succeeded in 

 discovering three of the members of the system, the inferior ones in the limited area of tin, 

 part of the valley of the Blackstone, confined to a trough hardh exceeding four miles in 

 length by two or two and a half in breadth. 



The annexed Bection exhibits the relation of the Taconic rocks of Smithfield and Cum- 

 berland, together with the adjacent rocks upon the west and east. 



Fig. 13. 



C. V. 



Granite, a. Altered magnesian slate. L. Limestone, b. Hornblende, c. Limestone, d. Dyke or thin bed of 

 hornblende, ten inches thick, e. Great bed of limestone. /. Altered 6late resembling serpentine, with small 

 paUl i substance. V. Valley of the Blackstone river, i. Granular quartz, interlaminated 



with siliceous slate. K. Conglomerate of the Coal formation, or it may be the conglomerate of the Old Red sand- 

 itone. 



