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MAGNESIAN SLATE. 
The color of this slate is usually light grey, with greenish patches. Sometimes it is 
dark, for the same reason that the preceding slate is so, namely, the presence of a decom¬ 
posing sulphuret. The broad layers into which the mass often readily splits, have a soft 
pearly lustre, and a soft unctuous feel. 
The magnesian slate, however, is not uniform in its characters. It passes into a rock, 
which at first view has been taken for mica slate ; but generally I believe it is not difficult 
to see that it is not really the latter rock. This is especially the case in the county of 
Berkshire, where there are some patches which very strongly resemble the finest varieties 
of mica slate. I certainly would not quarrel with a geologist, should he insist that some 
portions of this rock lying towards the Hoosic mountain are really and lithologically mica 
slate. In truth, at present it is a matter of perfect indifference with me. I do not consider, 
even if it should prove to be this peculiar rock lithologically, that it would affect the 
question of its age or place in the geological systems, or that it would throw this mass 
into the class of primary schists; for observation proves that such kinds of slate may be 
produced in any of the earlier periods, witness the so-called talcose slate in the Old Red 
sandstone of Cumberland in Rhode-Island. Its presence here shows conclusively that 
such a slate may be produced when the original materials of a suitable kind are furnished. 
Much of the ancient and primary aspect of the Rhode-Island and Mansfield beds is due 
to the character of the surrounding rocks, which have furnished the materials; though I 
by no means deny the agency of a high subterranean temperature in effecting certain 
changes. But I am not ready to admit that this is all, and that these peculiar varieties of 
rock could have been produced independent of their original materials. 
MINERAL CONTENTS. 
The Magnesian slate is very largely supplied with masses of milky quartz. So abundant 
indeed is this mineral, that it occurs in boulders over a wide extent of country where the 
slate is the principal rock. It is not in beds or veins, but it appears in irregular masses or 
bunches. Thin seams are not of unfrequent occurence. There is often a peculiar association 
of minerals in the Magnesian slate; thus, the quartz, though frequently pure milk white 
and opake, contains bunches of chlorite intermixed with the carbonate and oxide of iron and 
manganese. They usually appear upon the surface, like a disintegrating mass of a dark 
color, and of a spongy texture. This rock is far less fissile than the Taconic slate, and 
furnishes only the inferior kinds of flagging. It is less liable to decompose, and hardly 
furnishes, when decayed, a clayey mass like the preceding slates. 
After all, but little diversity of character is found in this rock, whether we examine it 
on the borders of the Sparry limestone, or along the eastern border of Massachusetts, and 
ranging side by side with the Hoosic mountain. 
The minerals which appear to lie peculiar to the talcose slate of the Gneiss system, as 
steatite, potstone, hornblende, etc., do not appear in this rock in New-York and Massa¬ 
chusetts. Of their actual appearance in this rock in one or two localities, I shall have 
