THE POLAR GLACIERS. -il 



with marine deposits. These alternations are sometimes very 

 numerous. There are as many as sixty distinct veins of consider- 

 able thickness, one over another, in the coal-mines of South 

 Wales, as also of Nova Scotia. There must have been, in that case, 

 sixty periods of dry land, each of sufficient duration to grow 

 many forests, and each followed by a long-continued submergence, 

 in order that each layer should become fossilized, and buried be- 

 neath a shale or a limestone, which could only have formed in 

 the depths of a quiet sea. The books say there were so many 

 upheavals, and a like number of subsidences, alternating with 

 each other. As if Old Earth had bent her back, for her load of 

 pit-coal, three-score times among the Welsh hills, and again as 

 many more at Halifax. It is a far more reasonable explanation, 

 that each considerable layer of coal indicates a cycle of long sum- 

 mers, and the withdrawal of a moderate depth of the oceans 

 from one hemisphere to the other, by reason of moderate accumu- 

 lations of ice in polar latitudes, arid the return again of the 

 waters after 10,500 years. In this way, and in no other that I 

 can conceive of, can be fairly explained the constant mixture and 

 alternations of terrestrial and marine relics, all through the fossil- 

 bearing formations, and the hundreds, if not thousands of differ- 

 ent and distinct strata which are found lying one above another. 

 Whoever, even cursorily, studies the phenomena of geology, 

 must be impressed with the enormous length of time it has taken 

 to arrange the terrestrial substructure, and prepare it for the 

 higher forms of life. Even the comparatively recent period of 

 the Bowlder Clay, which laid out the grounds of the present area 

 of civilization, dates back for its commencement, as we have seen, 

 probably 200,000 years. If it might be assumed that the Per- 

 mian or New Red Sandstone was formed during the next previous 

 period of extraordinary eccentricity, which was 850,000 years 

 ago, then the Devonian or Old Red Sandstone would come in, 

 very appropriately, at the next anterior era of extraordinary focal 

 distance, which occurred 2,500,000 years back. The Carbonifer- 

 ous period, which came between these two, could not have been 

 formed in less than 1,000,000 years, as most geologists concede ; 

 and by calculations previously indicated, those sixty Welsh layers 



