The researches of Halley and Adams have shown that from some cause, probably the result of gravity acting in conjunction with the varying eccentricity of the earth's orbit, the motion of the moon has been slightly accelerated as time went on, while the diurnal motion of the earth has been reduced by the action of the tides, and that the amount of this loss, in time, is equal to about one second in the length of our day, in 168,000 years. Now, this retardation in the earth's motion has not taken place at a uniform rate if caused by the reaction of the tides, as the nearer to the earth the moon was, the greater would be the tides, and, consequently, the greater would be the reaction; _i. e._, the retardation. But assuming that this retardation took place, on the whole, at twice the rate now prevailing, we would still have a period of six million years since the moon was thrown off by the earth, when our days were but three hours long. Turning from the theories of astronomy, which are obviously more or less inaccurate, owing to their very nature and the character and duration of the observations upon which they are based, we come to the nearer and more certain deductions of geology. Here we have the phenomena of denudation and deposition with which to deal, and inasmuch as these are measurable at many places, and under many conditions upon the earth to-day, it is safe to assume that computations made from these measurements cannot be far from the truth. We know that practically all of the great formations of the earth were depositions of material from water which contained them, and that, in many cases, heat caused these strata to be metamorphosed or crystallized ages after they were deposited, and that in this crystallization many of the fossils remaining imbedded in the deposited matter were destroyed. Concerning this deposition we know that it is going on to-day in the Atlantic and Pacific Oceans, where, in the deeper portions the Globigerina ooze is filling in these depressions with a deposit, resembling chalk, at the rate of perhaps an inch per century. We know that the Gulf of Mexico and several other ocean areas are being filled in with silt at the rate of as high as three inches per century. This silt is brought down in the tributary rivers and emptied into the gulfs. We also know that large areas in the Indian Ocean are being covered with coral and the débris from the coral reefs. We are absolutely certain that every geological period has had its characteristic fauna and flora, and that, in both the animal and vegetable kingdoms, some persistent types have connected it with both the past and the future, so that the fossils have become the "open sesame" to the geological records. We further know that the strata composing the earth's surface are subject to elevation and subsidence, such as is now going on in the delta of the Nile, on the coast of the Netherlands, and in many other places, and that such movement is a