1875.] ODt [Frazer. 



flow of the waters through the bedding we should be at a loss to account 

 for the absence of that flow along the planes of bedding. '■It is objected 

 in short to the hypothesis which would derive the limonite beds from the 

 disseminated pyrite in the overlying limestone. 1st. That the less the 

 limestone actually overlies, csetei'is paribus, the greater the extent of the 

 limonite deposits. 2d. There is no appearance of wasting in the lime- 

 stone commensurate with the effect produced, and not even the staining 

 from chalybeate waters which must have accompanied such a genesis. 

 3d. Very similar deposits are found in regions widely remote from the 

 limestone (thousands of feet of measures below it, — i. e., Hofacker's, 

 and the Cameron Iron Co.'s mine, &c,). 



The facts which are most intractable according to the former hypothesis 

 might have been predicted on the latter. A large portion of the slates 

 underlying the Auroral limestones are pyritiferous. A specimen taken 

 from a point on the Peach Bottom Railroad, about five miles southeast 

 of York was selected rather than one nearer to the limestone basin, 

 because in these latter tlie pyrite is distributed in crystals too minute to 

 be easily counted, while probably not differing materially in the 

 amount of iron contained. A slab of this slate 3^ X 2^ X I inches was 

 examined to ascertain the number of prints of pyrite crystals which it 

 contained. On the area of the surface 3|^ X 3^ = 8.75 sq. inches there 

 were counted 350 such pits visible to the naked eye. 



A micrometric measurement of a large number of these pits gave all 

 intermediate dimensions between j\ and ^^ of an inch. Assuming the 

 mean of the cubes of these dimensions or 0.00021 3 cubic inch as. the average 

 size of a crystal, we have 40 such crystals in 1 square inch, occupying 

 0.00851 cubic inch. In the specimen examined which was | inch thick, 

 there were nine layers distinctly visible to the naked eye. Each layer 

 was therefore 2V inch in thickness, and supposing only 0.00852 cubic inch 

 of pyrite in each square inch of laminse, we have 0.00852 X 24 X 12 X 5 

 = 12.27 cubic inches of pyrite in every square inch of area and 5 feet of 

 thickness of thesa slates. One cubic inch of pyrite weighs 126.1 grains, 

 la the above thickness and area of these slates there are then 1547.25 

 grains, or in each square foot of the same thickness 222803.57 grains = 

 31.81 lbs. 



This would give us for every mile of outcrop and 1000 feet of arch 

 above the present surface the enormous sum of 168,009,600 lbs. =^ 75,004 

 tons of 2240 lbs. But the metallic iron in this mass of slates one mile in 

 length and five feet in thickness would weigh 47729.7 tons, and supposing 

 it to be also oxidized, the anhydrous oxide would weigh 68185.2 tons and 

 as limonite 79691.5 tons. 



Assuming ^ of this to be washed into the soil and f to be left as earthy 

 iron ochre in the pits originally filled by pyrite in the slates still in place 

 and only partially decomposed, — which lie in juxtaposition to the ore ; 

 then every outci'op of these slates one mile long and one foot deep has con- 

 tributed about 20 tons to the deposits. But the entire mass of the rocks 



