158 The American Naturalist. [February, 
vania, the agent for their production was found in the gradual dying 
out of the heated area which involved the Appalachian system. Begin- 
ning at the Palisades and following a northwesterly line, Mr. Peckham 
notes the following facts in proof of his theory: Through eastern 
Pennsylvania the coal is metaphosed into anthracite. At St. Mary’s, 
on the summit of the Alleghanies, the coal is semi-anthracite. In the 
most easterly county of Pennsylvania in which petroleum is obtained, 
McKean, the petroleum occurs at a depth of two thousand feet, under a 
pressure estimated at four thousand pounds to the square inch, and 
filled with paraffine, just as it ought to be if produced by meta- 
morphism. Further west the petroleum becomes lighter. The pro- 
ducts of distillation are present in proper sequence along the entire 
line from Point Gaspé to Lookout Mountain, and the porous sand-bars 
and pebbly ripples formed by the currents of the primeval ocean are not 
filled with the oil, because they afford a receptacle adequate to receive 
and store the vast accumulations of distillate. (Amer. Jour. Sei., 
Dec., 1894.) 
Changes in Ore Deposits.—The chemical and physical changes 
that take place in ore deposits exposed to surface influences has been 
made the subject of study by Mr. R. A. F. Penrose, Jr., and the results 
of his investigations embodied in the following summary : 
The process of alteration is primarily one of oxidation, and generally 
of hydration, and both of these actions may go on alone, but generally 
both have their effect upon the same material. The action of surface 
influencesis in rare cases one of reduction. ‘The process of alteration 
frequently causes leaching of certain ingredients of the ore deposit. A 
worthless material may be made valuable by the introduction of a new 
constituent, as in Sige na ofa carbonate of lime bya phosphate 
oflime. D trated by capillary action in soils. 
The phy sical effect of superficial alteration is to make the deposit 
more open and porous, and to cause it to shrink. If, however, hydra- 
tion is active, expansion may be caused. 
The depth of alteration varies from a fraction of a foot to 1500 feet, 
and possibly more. 
The accumulation of soluble saline materials on the surface has an 
important effect in converting certain materials in underlying ore de- 
posits to chlorides, ete. This explains the abundance of haloid com- 
pounds in ore deposits of the arid regions of the western part of North 
America, and in certain parts of Chili and Peru. (Jour. Geol., Vol. 
II, 1894.) _ 
