Flinty Slate. 



263 



by Col. Joseph Totten of the U. S. army, who has become familiar 

 with the geology of that region, and to whose polite attentions I am 

 much indebted. 



The preceding rough sketch of the southwest part of Newport, 

 will give a correct idea of the relative position and extent of the four 

 or five rocks which are there associated, on a surface of four or five 

 square miles ; viz. granite, flinty slate, graywacke slate, limestone, 

 serpentine, and jasper. The flinty slate, it will be seen, occupies a 

 considerable space immediately contiguous to the granite, and it is 

 separated from the graywacke slate on that side, by a small ravine. 

 The flinty slate exhibits various degrees of induration, and more or 

 less of a mixture of different minerals. One variety has a gray 

 color, an imperfectly conchoidal somewhat splintery fracture, and is 

 rendered porphyritic by small grains of hyaline quartz. Another 

 dark gray variety exhibits greenish and white clouds. A third has 

 a reddish base of an earthy aspect and fracture, less hard than the 

 preceding, and containing numerous light colored, rounded masses, 

 resembling hornstone, from the size of a pin's head to that of a mus- 

 ket bullet ; giving it an amygdaloidal aspect. If hard enough to re- 

 ceive a polish, it would form an elegant ornamental stone. A third 

 variety exhibits a semi-crystalline aspect, and contains minute scales 

 of mica. This variety is traversed by veins of granite, composed of 

 quartz and flesh-colored feldspar. (Nos. 380 to 383.) 



For the most part, this rock exhibits scarcely no marks of stratifi- 

 cation. But not unfrequently, even in the most highly indurated 

 masses, the traces of a former slaty structure are distinctly visible. 

 In short, it is quite obvious, that it is the graywacke slate, which has 

 been subject to a heat so powerful as to indurate, and for the most 

 part, to melt it. I think it would be easy to collect specimens exhib- 

 iting almost every gradation from graywacke slate to flinty slate. 



In the southeastern part of the above sketch, the granite cuts off 

 the graywacke slate at right angles to the general course of the lay- 

 ers : and the slate is indurated only a few feet from the junction. 

 The junction between the granite and the siliceous slate is obvious in 

 several places, particularly at a ledge at the southwest extremity of 

 the granite : and the two rocks are so firmly united as to separate no 

 easier than in any other direction. 



The graywacke slate of this spot has generally the shining or 

 glazed appearance of the oldest varieties of argillaceous slate : but 

 in the extensive excavations that have been made in it for the con- 



