minerals as the rocks they rest upon. For instance, granite is very commonly the foundation rock; but immediately upon this repose thick beds of gneissoid rocks. Now gneiss, like granite, is composed of quartz, feldspar, and mica, and differs only in this—that the constituents have been broken up, assorted by water, and redeposited in regular layers. As we have different varieties of granitoid rocks, so we have corresponding varieties of gneissoid rocks, differing from the former only in being stratified. So general and so well recognized is this phenomenon, that Sir Roderick I. Murchison, an eminent geological authority, designates these lower strata beds of "fundamental gneiss." This occurrence of gneiss, every where reposing upon granite, is a most interesting and instructive fact, and confirms all that I have said of the denudation of the primitive islands, and the universality of the primitive sea.

But, though gneiss is generally the foundation stratum, we find abundance of other rocks either reposing upon the gneiss, or interstratified with it in the lower portions of the sedimentary series. Undoubtedly some of these have resulted from the impalpable powder to which long-continued attrition reduced some portions of the primitive granite, transported to the remotest and quietest portions of the ocean, and there allowed to subside. But we know also that others of the oldest strata associated with the gneisses have been the results of chemical agencies. This is one of the revelations of modern chemical geology, which no name has more adorned than that of Dr. T. Sterry Hunt, of the Geological Commission of the Dominion of Canada. According to Hunt and Logan, the limestones of this early period could have had no other than a chemical origin. Common limestone is composed, as every one knows, of carbonic acid and lime. Heat, as the manufacturer of lime

illustrates, expels the carbonic acid in the form of a gas. Under the high temperatures of the earliest periods, therefore, limestone could not exist. It has already been stated that all the carbon, sulphur, and chlorine in existence must, in those periods, have been represented by carbonic (CO2), sulphuric (SO), and chlorhydric (HCI) acids, existing in a volatile state, mingled with the other gaseous constituents of the atmosphere. At the same time, all the silica of the globe, playing the part of an acid, would unite with the fixed elements, producing silicates of complex constitution -just such silicates as we actually find entering into the structure of the oldest portions of the earth's crust. The first rains which descended would be charged with the atmospheric acids just mentioned, which, attacking the solid silicates at a high temperature, would, as the analytical chemist knows, produce reactions resulting in the chlorids. of calcium (ClCa), magnesium (CIMg), and sodium (CINa), mingled with the sulphates of these bases (SO3KO, SO3NaO, SO3CaO, SO3MgO). The liberated silica (Si203) would separate, and would be chemically precipitated during the subsequent cooling of the waters, and would thus give rise to the enormous beds of quartz which we actually find among the very oldest strata, but nowhere else.

Among the other silicates originally formed is a family of minerals known as feldspars-very abundant, and containing, besides alumina, large percentages of either potash, soda, lime, or lithia, or two of these alkalies together. The decomposition of these feldspars-especially orthoclase, or potash-feldspar (Si2O3Al2O3KO)-must have taken place on an extensive scale. The result would be a clayey hydrate, called kaolin (Si2O3Al2O3) when pure, which became the basis of many clays and other argillaceous rocks like graphic and roofing slates. The remainder of the orthoclase. would be in the form of silicates of potash (Si2O3KO) and

soda, which would remain in solution in the sea. But the carbonic acid of the atmosphere, having a more powerful affinity for these alkalies than the silica, would wrest them from combination with the silica, as already stated, and would form carbonates of potash (CO2KO) and soda (CO2NaO), while the silica would be added to the quartzose rocks of the globe. These carbonates, whether formed in the ocean or on the hill-sides, would, when transported to the ocean, find themselves confronted with chlorid of calcium (CICa), and probably other chlorids. Chlorid of calcium, carbonate of potash (CO2KO), and carbonate of soda (CO2NaO), brought face to face, would immediately enter into arrangements for an exchange of partners. Carbonic acid (CO2) would incontinently abandon potash (KO) and soda (NaO), and betake itself to calcium (Ca), changing its name, by the aid of a little oxygen, to "lime" (CaO), and forming a union known as carbonate of lime (CO2CaO). With equal celerity, chlorine (Cl), dispossessed of its calcium (Ca), would compensate itself by seizing upon potash (KO) and soda (NaO), and, after eliminating the oxygen (O) in their constitution, would unite with potassium and sodium, forming chlorid of potassium (CIK) and chlorid of sodium (CINa). Thus all parties would be better satisfied, and each would abide in its appropriate place. Carbonate of lime (CO2CaO) refusing, for the greater part, to be dissolved in sea-water, would settle to the bottom and become limestone; while chlorid of sodium (CINa)-which is only the chemist's name for "common salt”—remained in solution, and thus gave its characteristic salinity to the sea. Chlorid of potassium (CIK) also continues to exist in sea-water in smaller quantity.

The diagram on the following page is intended to represent to the eye the chemical reactions above described. The symbols are familiar to the chemical reader; but they

will be rendered intelligible to all by the explanations in

the text.

There seems to be but little poetry in the attempt to unravel the thread of chemical reactions which followed each other upon the earth in those dim and twilight ages; but it is certainly an inspiring development of late researches that the sceptre which chemistry sways over the modern world is the same which she wielded over the mute atoms of the forming crust.

It appears, from what has been suggested, that a portion of those ancient strata originated from sediments mechanically deposited, and another portion from chemical precipitates thrown down while the elements were adjusting themselves according to their strongest affinities.

The reader should not imagine that the proofs of these things are afar off. They lie within the scope of his own observation and verification. If you can not gaze upon the frowning summit of Katahdin, or the dark and lichencovered sides of the Adirondacs, nor the upturned piles of stony lumber which make the ridges of the Appalachians, nor the acres of rocky floor torn up for your inspection along the shores of the upper lakes, examine some of the specimens which Nature has brought from those northern regions to your very doors. Scattered over your fields may be found fragments of the underlying unstratified granite and sienite, diorite and dolèrite. Here, too, are fragments of rocks formed of the same constituents as these, but under a stratified arrangement. The most striking of these are the gneisses, where the various colored minerals set forth the stratification with distinctness. These came from the thick beds resting upon the crystalline foundation of the earth's crust. They are the ruinsa second time ruined-of some ancient rocky shore which the fury of the elements has reduced to sand. Here are