MAGNESIAN SLATE. 77 



occasion to speak hereafter. We find, however, needleform schorl, octahedral iron, and 

 sulphuret of iron in unmodified cubes, both in Williarnstown (Massachusetts) , and Arlington 

 (Vermont) . 



RANGE AND EXTENT. 



In my Report, I have spoken of two ranges of this rock, which I supposed to be two 

 masses, or might be made out as such, one on each side of the Stockbridge limestone. I 

 here speak of the main bed of limestone, for thinner and less important ones exist. 



The mountains composed of this rock are the highest in the Taconic ranges, rising from 

 one to three thousand feet. Saddle mountain, between Williarnstown and Adams, is 

 twenty-seven hundred feet above the Hoosic, and thirty-four hundred above the level of 

 the sea, or the tide water at Albany. A range of mountains composed of this slate extends 

 along the western border of Massachusetts, and through Vermont. It often rises to the 

 height of fifteen hundred feet. This range is known as the Taconic range, and has fur- 

 nished the name to the system of rocks I am describing. 



From these considerations, it appears that there are two parallel ranges of mountains 

 which are composed principally of this rock. Thus the range at the western base of the 

 Hoosic mountain, in which Saddle mountain is the highest point, is the first. The second 

 is the range four or five miles west : it is inferior in height through its entire extent. The 

 two ranges are connected by lateral spurs ; and sometimes, in consequence of their close 

 position, they seem to coalesce, and to obliterate as it were the intervening valleys. 



The Magnesian slate is one of the most permanent and extensive members of the 

 Taconic system. It crosses the Hudson about thirty miles above the city of New- York, 

 and passes south through New-Jersey into Pennsylvania, beneath the New Red sandstone, 

 under which rock it disappears near Stony point upon the Hudson river. It ranges north 

 as far as my knowledge extends, having seen specimens of it from the townships in Canada 

 East. It is parallel to the preceding slate, ranging N. 10°- 15° E., with a dip of from 

 fifty to eighty-five degrees. 



It is not known to contain veins of the oxides or sulphurets of the metals : it only con- 

 tains those bodies in disseminated particles. In the regions which have been spoken of, no 

 trap dykes are known to traverse this rock ; a fact which is remarkable, when we take 

 into view the great extent of the country over which it is a prominent rock. 



The breadth of country over which it prevails is not much less than fifteen miles, leaving 

 out of consideration the Stockbridge limestone and Brown sandstone or Granular quartz. 

 Its absolute thickness cannot be determined with any certainty : it is undoubtedly great, 

 and ranks in this respect with the primary schists. No trace of organic bodies has hitherto 

 been found in this rock. 



The relations of this rock are given in Fig. 7 (page 63) , and also on Plate XVIII. 



This slate disintegrates slowly : it forms a flat gravel, but more tenacious of water by 

 far than siliceous gravel. By itself, or unmixed, it makes a poor soil ; but when com- 



