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184 of climate which we thus anticipate, but, if we mistake not, in continually-lessening force and extent the farther back we go. For, long ages previous to the recent glacial epoch, through all the Tertiary era, the fossil plants and animals indicate the prevalence of a warm and genial climate over the greater part of the globe. Then come the chalk-beds of the Cretaceous period, in which are frequently found water-worn blocks of granite and aggregations of pebbles, proving that then, as now, the iceberg floated down from the north over seas that were quietly depositing the chalk-shells. Still older is found a long series of secondary strata, the Oölite, the Lias, and the Trias, which were deposited in at least sub-tropical climates. They are the burial-grounds of the enormous saurian reptiles that once had an age all to themselves in the world's chronology. Their remains have been found within a thousand miles of the north-pole, thus proving that warm seas covered every zone.

Between the great divisions of Secondary and Primary in geology, there lies a stratum found only in the higher half of the latitudes, and known as the Permian or New Red Sandstone. The scanty life-forms found in it, and the coarse grit and angular bowlders of which it is composed, evince the well-known glacial action. Geologists generally think that there elapsed between these great divisions a very long period of time in which, excepting the sandstone, but little was done one way or another to build up the crust of the earth or leave a mark in its records. This doubtless indicates periods of very small eccentricity. Such periods did occur, according to Mr. Croll's calculations, immediately before and after the great eccentricity of 850,000 years ago, in which we may perhaps conjecture the New Red Sandstone to have been formed.

Previous to this age were the long Carboniferous periods, during all of which a warm and moist climate prevailed over all lands that have yet been explored. Below the coal-measures are found again the grits and bowldery conglomerates of the Old Red Sandstone, which, with great paucity of organic remains, would imply the alternations of somewhat glacial climates. The Silurian, Cambrian, and Laurentian systems preceded the Old Red in the order named, and reach back to the dawn of life on the earth. These formations are of vast thickness, and were deposited at the bottom of warm seas in all parts of the world.

It cannot be denied that, as we go back in the geologic records, we find more and more the evidences of greater heat and a more equable climate. It is certain that the astronomical relations which we have pointed out—the revolutions of the orbital points and the alternations of great and small eccentricity—have never ceased to exist. Therefore, if the world had been subjected to only the same solar heat in ancient as in recent periods, there must have been repeated glacial epochs; and we should find the bowlder, and the