92 TACONIC SYSTEM IN RHODE-ISLAND. 



Still preserves the general character of the Magnesian slate, and is a perfect example of it 

 througliout most of its body. 



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

 covered in this narrow basin or trough. As the granite appeared in a heavy body upon 

 the west of the slates and limestones, I pursued an easterly route for the discovery of other 

 members of the system. I was led upon this direction, too, from having seen boulders of 

 brown sandstone in the drift 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 route from Smithfield to Cumberland, the quartz, if it exists, is concealed beneath 

 thick beds of drift. The quart-j is upon the eastern side of the Blackstone. As developed 

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

 nating with a species of magnesian slate, but of a darker color and more siliceous than this 

 rock usually is. The 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-five of slate, which, how- 

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

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

 at five hundred feet. 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 )nile north of Whip- 

 ple's, the trend is N. 55° 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 slate, limestone and quartz, on a route which is nearly perpen- 

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

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

 I made no 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 this 

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

 length by two or two and a half in breadth. 



The annexed section 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 slate resembling serpentine, with small 

 patches of cpidotic looking 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- 

 stone. 



