186 A. P. COLEMAN DRY LAND IN GEOLOGY 



Our Pleistocene ice age, with its array of glacial and interglacial beds, 

 was merely an imitation on a much smaller and less impressive scale of 

 the tremendous .Paleozoic ice age, which laid down in places 1,000 feet or 

 more of till and included interglacial times long enough to form great 

 coal seams, as in the Greta beds of New South Wales. 



These ancient boulder-clays and moutonnees rock surfaces of the south- 

 ern continents bring us face to face with the most dramatic moment in 

 geology, when a world enervated by the moist, hot-house conditions of the 

 earlier Carboniferous found itself in the grip of the fiercest and longest 

 winter of the ages, followed by the merciless droughts of the Permian 

 and Triassic. 



Late Pkecambeian Ice Age 



Still more ancient tillites have been found in a number of regions, 

 sometimes described as Lower Cambrian; at others as uppermost Pre- 

 cambrian. In a few cases Cambrian fossils have been collected in beds 

 above the tillite, but, so far as I am aware, never beneath it. It is possi- 

 ble that there were two early ice ages, with an interval between; but it 

 seems more probable that they are of the same age and all really Pre- 

 cambrian. The Australians believe that their more ancient tillites are 

 Cambrian, however. 



Tillites have been suggested at two places in the KeweenaAvan of Amer- 

 ica. They occur in the Gaisa beds of Norway, where there is a striated 

 surface beneath; perhaps also in the Torridonian of Scotland. In Aus- 

 tralia Howchin describes an area of 460 miles by 250, and they are found 

 also in Tasmania. They are reported from the Nant'ou formation in 

 China; the Griquatown series in Cape Colony, where they have an area 

 of at least 1,000 square miles, and near Simla, in India. The last two 

 mentioned may be older than the Keweenawan. Sir Thomas Holland 

 thinks the Simla tillite may even be as old as the Huronian. 



These tillites belong to higher latitudes than those of the Permocar- 

 boniferous, none coming nearer the equator than 29°; but some of them 

 occupy regions noAv warm temperate, while the ice-sheets of the Pleisto- 

 cene halted at about 38° in North and South America and 52° in Europe. 

 In so old a period one can hardly expect to find very complete evidence 

 of the area covered by glaciers; but this ice age seems to have been more 

 severe than that of the Pleistocene. 



Huronian Ice Age 



Much farther off in the abyss of Precambrian time is the Lower Hu- 

 ronian Glacial period, thus far known with certainty only from the Cana- 



