TACONIC SYSTEM IN RHODE- ISLAND. 93 



The (rap dyke represented in this section has the aspect of hornblende, but it has also the 

 soapy feel of many of the varieties of the trappean rocks. Of the altered magnesian slate 

 on the east of the limestone beds, I ought to say that while it would not be difficult to 

 selivi tolerable specimens of serpentine, talc and epidote, still as a whole there is nothing 

 differing much from the rock, very distinctly developed. Those individual minerals are 

 merely slight changes in a rock originally magnesian ; but how much of these apparent 

 changes are due to the nature of the original materials of the rock, and how much to meta- 

 morphic action, does not clearly appear even from an inspection of the rocks themselves. 



In conclusion, I remark that we have in this region a fragment of the Taconic system. 

 The limestone is inclosed in magnesian slate, as in Berkshire (Massachusetts) , and the 

 quartz is also accompanied with a slate whose characters reminded me strongly of that 

 associated witli the quartz rocks of Stone hill in Williamstown. It is to be borne in mind, 

 however, thai these rocks are modified by intruded igneous masses. But then these acci- 

 dents, even although taken in connection with the limited extent of the rocks, do not 

 destroy the system : they ought still to be considered as representatives of it. That they 

 have been vastly more extensive than their present area, is proved by the immense quan- 

 tity of their fragments which fill up, as it were, the valley of the Blackstone; and, in 

 addition to this, they seem to form by far the greater portion of the materials of the Coal 

 formation, especially the conglomerate, which is made up of granular quartz, and cemented 

 by the magnesian slate. 



From these two facts, it appears that these rocks have for a long time been subjected to 

 the action of those agents which destroy the already consolidated materials. We need not 

 wonder, then, at the small space which they occupy ; though it must be recollected that 

 they have furnished materials for another system, as well as an immense amount of debris 

 in the valley of the Blackstone. 



The character of the soil arising from the decomposition of the rocks I have now 

 described, resembles very closely that of Berkshire (Massachusetts) , and of many other 

 localities where the same rocks occur. One of the results of the decomposition of the 

 slaty limestone, is the formation of yellow soil, in which yellow ochre predominates very 

 largely : it is a result identical with that which has taken place in the Taconic range, 

 though upon a much larger scale. The result I refer to, is the formation of the hematite 

 beds'; and it appears from this and many other examinations I have made, that this ore is 

 one of the products of these slaty limestones, or those in which talc abounds, and with 

 which we always meet with more or less of ferruginous matter. 



