THE POLAR GLACIERS. 39 



then, as now, the ice-berg 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 Oolite, 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 w T hich 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, except- 

 ing this sandstone, but little was done one way or another to 

 build up the crust of the earth, or to 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, dur- 

 ing 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 the 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 de- 

 posited 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 



