Limestone in Smithfield, fyc. 



311 



Unite, according to Professor Webster : also talc in veins at Bolton 

 as well as at Littleton. 



Very delicate and beautiful amianthus is found in veins in the 

 limestone, about two miles south west of the centre of Chelmsford. 

 The fibres are sometimes two or three inches long, and resemble the 

 finest and most beautiful white silk. The same mineral in small 

 quantities is found at Bolton. (Nos. 523, 524.) 



Limestone in Smithfield, R. I. 



There are two principal beds of this rock, a little more than a mile 

 apart; the most easterly one, half a mile from Blackstone river, 

 called the Dexter rock, and the other, the Harris rock. I have ex- 

 amined only the latter ; and this occurs in that variety of hornblende 

 slate, which the Werenians call greenstone slate, and transition or 

 primitive greenstone. The slaty structure of a part of the rock is 

 quite obvious, though to a cursory observer, most of the mass resem- 

 bles very much secondary greenstone. I am satisfied that the Dex- 

 ter rock occurs in the same slate, which, in fact, appears to be the 

 talco-chloritic slate of that region, passing into hornblende slate. 

 Though the parallel division of the hornblende slate be evident, yet 

 the limestone is destitute of stratification ; forming an irregular mass, 

 penetrated by projections from the slate. It is white and distinctly, 

 though not very coarsely granular and crystalline. Some of it is do- 

 lomite. (Nos. 498 to 500.) It may be, and has been wrought as mar- 

 ble ; though it is difficult to obtain large blocks without fissures. 

 Sometimes it is clouded. (No. 497.) 



The imbedded minerals in this limestone are, with few exceptions, 

 very different from those just described in the limestone beds in 

 gneiss in Massachusetts. In the Smithfield rock, talc is one of the 

 most abundant of the minerals, and it is often of a rich silvery white 

 color, associated w T ith large prisms of rhomb and calcareous spar. 

 Some of the nacrite found at the Dexter rock is beautiful. Nephrite 

 exists here, also, in veins and nodules : also limpid quartz in crys- 

 tals ; calcareous and brown spar, tremolite and asbestus. 



If, as seems to me extremely probable, the hornblende rock in 

 which this limestone occurs, has been subjected to the action of 

 powerful heat, we have a cause for the want of stratification in the 

 latter. And the occurrence of immense quantities of sienitic granite 

 in the vicinity, shows us whence the heat might have been derived. 



