who would earn distinction rather by overthrowing the work of their seniors than by building on it. These writers base their conclusions on a few exceptional facts, as the occasional occurrence of seams of coal without distinct underlays, and the occurrence of clay partings showing aquatic conditions in the substance of thick coals; and they fail to discern the broader facts which these exceptions confirm. Let us consider shortly the essential nature of coal, and some of the conditions necessary to its formation. A block of the useful mineral which is so important an element in national wealth, and so essential to the comfort of our winter homes, may tell us much as to its history if properly interrogated, and what we cannot learn from it alone we may be taught by studying it in the mine whence it is obtained, and in the cliffs and cuttings where the edges of the coaly beds and their accompaniments are exposed. Our block of coal, if anthracite, is almost pure carbon. If bituminous coal, it contains also a certain amount of hydrogen, which in combination with carbon enables it to yield gas and coal tar, and which causes it to burn with flame. If, again, we examine some of the more imperfect and more recent coals, the brown coals, so called, we shall find that in composition and texture they are intermediate between coal proper and hardened or compressed peat. Now such coaly rocks can, under the present constitution of nature, be produced only in one way, namely, by the accumulation of vegetable matter, for vegetation alone has the power of decomposing the carbonic acid of the atmosphere, and accumulating it as carbon. This we see in modern times in the vegetable soil, in peaty beds, and in vegetable muck accumulated in ponds and similar places. Such vegetable matter, once accumulated, requires only pressure and the changes which come of its own slow putrefaction to be converted into coal. But in order that it may accumulate at all, certain conditions are necessary. The first of these includes the climatal and organic arrangements necessary for abundant vegetable growth. The second is the facility for the preservation of the vegetable matter, without decay or intermixture with earthy substances; and this, for a long time, till a great thickness of it accumulates. The third is its covering up by other deposits, so as to be compressed and excluded from air. It is evident that when we have to consider the formation of a bed of coal several feet in thickness, and spread, perhaps, over hundreds of square miles, many things must conduce to such a result, and the wonder is perhaps rather that such conditions should ever have been effectively combined. Yet this has occurred at different periods of geological history and in many places, and in some localities it has been so repeated as to produce many beds of coal in succession.