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[Assembly 
also abound, and there are at least two important localities of the lenti- 
cular clay iron ore. In regard to the gypsum, it may be stated that a 
specimen from a bed owned by Mr. Thomson, of Springport, which 
was analyzed at his request, gave the following results in 100 grains, 
freed from water, viz. 
Sulphate of lime, 71.75 
Carbonate of lime, 21.65 
Silica and alumina, (clay) colored by oxide 
of iron,... 6.60 
Most of the western plaster is probably similar in its composition. 
It usually effervesces with acids, owing to a portion of carbonate of 
lime which it contains. The bed from which the above specimen was 
procured yields about 2000 tons annually, nearly all of which is used 
at Springport as a manure. It is of a dark grey or nearly black colour, 
intermixed with thin scales of transparent selenite. On exposure to 
the air it disintegrates and is peculiarly interesting on account of the 
layers of pure sulphur, in a semicrystalline form, which pass through 
it. Although the occurrence of this mineral is not uncommon in the 
gypseous beds of the West, I have never met with such well characteri- 
zed specimens as in the present instance. 
To the above minerals may be added petroleum found on Cayuga 
Lake of the same kind as that of Allegany county, though it is less 
abundant. Rounded masses also occur in the slate near Aubuin and 
elsewhere, which when broken exhibit seams of sulphate of barytes, 
radiated and of a snow-white colour, These masses are composed 
chiefly of carbonate of lime and are usually known by the name of 
septaria, in consequence of their being divided into distinct portions by 
partitions or septa. 
Among the useful minerals of this county is to be reckoned water 
limestone, which, as well as the rock above it, contains fluor spar in 
small crystals, calcareous tufa is found in Sempronius, and sulphate of 
iron and sulphate of magnesia, are also to be included among the mi- 
nerals of this county ; as they are formed on some of the shales by 
the spontaneous decomposition of the substances which they contain. 
Messrs. Vanuxem and Hall found associated with petroleum, near 
Ogden's Ferry, a liquid substance of the colour of phosphate of iron 
or Prussian blue, and another like spermaceti before the oil is fully 
