TACONIC SYSTEM IN RHODE-ISLAND. 
93 
The trap 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 
select 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 with the quartz rocks of Stone hill in Williamstown. It is to be borne in mind, 
however, that 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 tire 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. 
