86 PROCEEDINGS OF THE ACADEMY OP 



phyry mountam in all directions. This mountain covers at its 

 base about seventy acres, more or less, and is furrowed by deep cuts 

 near its summit ; some of tliese to a depth of eighty to one hun- 

 dred feet. The best and purest ore is that which was found lying 

 on the surface of its slopes, and of this there is still a very large 

 quantity; but the large boulders have been almost all removed, 

 while that which remains is so finely divided and so mixed with 

 the clay and soil that any ordinary method of separation would 

 make it too expensive. 



Lately, the California hydraulic mining has been applied to 

 win this ore, with great success. Water is pumped through large 

 hoses which are led up the sides of the hills, and the debris is 

 washed down through sluice-boxes and over small falls, which 

 agitate it sufficient!}' to shake the ore from the dirt and allow it 

 to deposit at the foot of the hill by virtue of its higher specific 

 gravity, in receptacles provided for it. The remaining ore is ob- 

 tained by blasting, is loaded on a gravit}' railway and carried to 

 the foot of the mountain, where it is dumped, three or four tons 

 at a time, over a shoot which precipitates it some eight or ten 

 feet, upon the flats of the Iron Mountain Railroad Company, which 

 are awaiting it. The shock as this heavy weight strikes the cars 

 is great enough to cause them sometimes to tilt over on two 

 wheels. How much it increases the wear and tear I was unable 

 to ascertain. 



This ore contains from 65 to 68 per cent, metallic iron, asso- 

 ciated with 0.031 per cent, to 0.11 per cent, phosphorus and 4 to 

 4.5 per cent, silica, and a trace of sulphur. The quantity exposed 

 is enormous, but was stated by Mr. David Thomas, of Catasauqua, 

 not to equal in quantity the celebrated Cornwall mines of this 

 State. 



The ore from Pilot Knob is much more sandy than that from 

 Iron Mountain. It occurs in a bed dipping with the general dip 

 of the country rock, and inclosed within the porphyry out of 

 which the knob is formed. The formation of this ore is a most in- 

 teresting study, and the only plausible theory seems to be that of 

 lateral replacement, a case of metasomatism wiiere the porpliyry, 

 having become slaty in structure, and less capable of resisting 

 the solvent, has been replaced along the line of strike, and only 

 in such laminated parts. Tiiis ore is banded in appearance, and 

 is almost, if not quite, invariably hematite. 



June 16. 



The President, Dr. Ruschenberger, in the cliair. 



Twenty-five members present. 



Notice of some Fresh-wafer and Terrestrial Ehizopods. Prof. 

 Leidy stated that among the amoeboid forms noticed by him in 



