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field, and Johnston, marked as " hornblende . rock " on the 

 geological map of Rhode Island prepared by Dr. C. T. Jackson 

 and accompanying his Report on the Geology and Agriculture of 

 that State (1839) ; and, like the talcoid band west of the Con- 

 necticut, they appear to possess lithological characters belong- 

 ing partly to the Huronian series and in part to the Montalban. 

 According to Dr. Jackson these rocks are substantially the 

 same throughout their distribution. I have examined them in 

 Smithfield, where they consist largely of fine-grained, little 

 micaceous mica slate, approaching argillite, and closely re- 

 sembling much of the Montalban mica slate of the Nashua and 

 Merrimac Valleys in Massachusetts. And interstratified with 

 this slate are large beds of chlorite slate, fine-grained, green, 

 and soft, and dark-colored, obscurely crystalline, slaty-looking 

 hornblendic rocks, and other rocks having, frequently a quartz- 

 itic, and sometimes a felsitic, appearance. The limestone de- 

 posits of Smithfield and adjoining towns, some of which are 

 quite extensive and of considerable economic importance, be- 

 long in this series, and are enclosed in the rocks above named. 

 The limestone appears to be stratified, is usually more or less, 

 frequently largely, magnesian, and contains a good variety of 

 accessory minerals, among which talc is, perhaps, the most 

 abundant ; and Dr. Jackson states that limited beds of talc are 

 of frequent occurrence in other portions of this series. All these 

 rocks, including the limestone, have the same general strike 

 and dip throughout, and appear to be conformable in this respect 

 with the enclosing Montalban gneisses. Strike, S. 45°— 60° E. ; 

 dip, N.E., steep. Associated with these stratified rocks, and 

 occurring abundantly in the interval between the principal beds 

 of limestone, is a rather fine-grained, apparently exotic, granite. 

 It is hornblendo-micaceous ; and, although probably a Montalban 

 granite, it cannot be regarded as a typical variety. The proof of 

 the Montalban age of this series of rocks is found mainly in 

 their stratigraphic relations to the bordering gneisses, and in 

 the small disturbance which they exhibit as compared with even 

 the least disturbed of our Huronian beds. Relative disturbance 



