Prof. S.F. Peckham, who has studied the petroleum field of southern California, attributes the abundant hydrocarbon emanations in that locality to microscopic animals. It is quite possible that this is true in this and other localities, but the bituminous shales which are evidently the sources of the petroleum of Pennsylvania, Ohio, Kentucky, etc., generally contain abundant impressions of sea weeds, and indeed these are almost the only organisms which have left any traces in them. I am inclined, therefore, now, as in my report on the rock oils of Ohio, published in 1860, to ascribe the carbonaceous matter of the bituminous shales of Pennsylvania and Ohio, and hence the petroleum derived from them, to the easily decomposed cellular tissue of algæ which have in their decomposition contributed a large percentage of diffused carbonaceous matter to the sediments accumulating at the bottom of the water where they grew. In a recent communication to the National Academy of Sciences, Dr. T. Sterry Hunt has proposed the theory that anthracite is the result of the decomposition of vegetable tissue when buried in porous strata like sandstone; but an examination of even a few of the important deposits of anthracite in the world will show that no such relationship as he suggests obtains. Anthracite may and does occur in sedimentary rocks of varied character, but, so far as my observation has extended, never in quantity in sandstone. In the Lower Silurian rocks anthracite occurs, both in the Old World and in the New, where no metamorphism has affected it, and where it is simply the normal result of the long continued distillation of plant tissue; but the anthracite beds which are known and mined in so many countries are the results of the metamorphism of coal-beds of one or another age, by local outbursts of trap, or the steaming and baking of the disturbed strata in mountain chains, numerous instances of which are given on a preceding page. M. Mendeleeff, in his article already referred to, misled by a want of knowledge of the geology of our oil-fields, and ascribing the petroleum to an inorganic cause, connects the production of oil in Pennsylvania and Caucasia with the neighboring mountain chains of the Alleghanies and the Caucasus; but in these localities a sufficient amount of organic matter can be found to supply a source for the petroleum, while the upheaval and loosening of the strata along lines parallel with the axes of elevation has favored the decomposition (spontaneous distillation) of the carbonaceous strata. It should be distinctly stated, also, that no igneous rocks are found in the vicinity of productive oil-wells, here or elsewhere, and there are no facts to sustain the view that petroleum is a volcanic product.