74 GEOLOGY AND MINERALOGY. 



called his attention to the rapid decomposition of limestone 

 and clay schists of Caledonia and Orleans connties. 



Within the calcareous and mica slate region, (so named 

 by Prof. Adams,) there is an upheaval, or range of gran- 

 ite, of a very peculiar character. It is first seen on the 

 east side of Lake ]Memphremagog in Stanstcad, P. Q. and 

 from thence may be traced through Derby, Salem, Brown- 

 ington, Irasburgh, Albany and Craftsbury, and probal)ly 

 extends to Xorthlield in Washington County. In this 

 ransre are some curious forms differiliu: from most of the 

 irranite in the state. There is the tabular or jointed vari- 

 ety of granite of great beauty. All granite is jointed more 

 or less, but the divisional phmes are usually quite irregu- 

 lar, yet, in the variety under consideration, those planes 

 are essentially parallel. The result is, that the mass is di- 

 vided into tables often of large dimensions, but sometimes 

 there are three sets of joints, and the blocks have a rhom- 

 boidal form. When the tables are thick, there is only 

 one set of seams, and long columns can easily be got out." 

 A magnificent development of these, may be seen at the 

 south-west corner of Irasburgh where colunms eighty feet 

 long and three or four feet thick might easily be procured. 

 " The tabular variety of granite is very common in the de- 

 posits of this rock, south of Lake jMemphremagog in Cov- 

 entry" and Brovvnington. The quantity in Irasburg would 

 suffice to build a city, but has as yet, never been quarried. 

 At some future period it will be regarded of immense val- 

 ue. It is within a mile of Black Kiver. 



Another variety of granite is called by Dr. Hitchcock, 

 "concretionary." The basis of this remarkal)le variety, is 

 rather fine grained, Avhite and highly feldspathic. Tli(>. 

 mica however, is usually dark, and when it exists in large 

 quantity it gives rocks the aspect of syenite, but there is 

 no hornblende present. Scattered through this base, oc- 

 cur numerous spherical or elongated and somewhat flat- 

 tened nodules of black mica from half an inch to two inches 

 in diameter, and when elongated, the larger axis is some- 

 times seen as much as four or five inches long. They are 



