194 FroceccUngs of the Royal Physical Society. 



strata any evidence of alternating cold and warm epochs. 

 So long as ocean-currents from the tropics found ready 

 entrance to polar regions across vast tracts of what is now 

 dry land, extreme and wide-spread glacial conditions were 

 impossible. Any lowering of temperature due to cosmical 

 causes might indeed induce new snow-fields and glaciers to 

 appear or existing ones to extend themselves in northern 

 regions and the most elevated lands of lower latitudes. But 

 such local glaciation need not have seriously affected any of 

 the areas in which coal-seams were being formed. For 

 nothing appears more certain than this, that our coal- 

 seams as a rule were formed over broad, low-lying, alluvial 

 lands, and in swamps and marshes, along the margins of 

 estuaries or shallow bays of the sea. Some seams, it is true, 

 are evidently formed of drifted vegetable debris, but the 

 majority point to growth in situ. The strata with which 

 they are associated are shallow-water sediments which 

 could only have been deposited at some considerable 

 distance from any mountain-regions in which glaciers were 

 likely to exist. It is idle, therefore, to ask for evidence of 

 oflacial action amonsjst strata formed under such conditions. 

 The only evidence of ice-work we are likely to get is that of 

 erratics. And these are not wanting, although it is pro- 

 bable that most of those which are found embedded in coals 

 have been transported by rafts of vegetable matter or in the 

 roots of trees. The same explanation, however, will not 

 account for the boulders which Sir William Dawson has 

 recorded from the coal-fields of Nova Scotia. He describes 

 them as occurring on the outside of a gigantic esker of 

 Carboniferous age, and thinks they were probably dropped 

 there by floating ice at a time when coal-plants were 

 flourishing in the swamps on the other side of the gravel 

 embankment. 



If the disposition of the land-areas in Carboniferous times 

 rendered such an ice age as that of the Pleistocene impos- 

 sible—in other words, if the effects flowing from high 

 eccentricity of the orbit must to a large extent have been 

 neutralised — the flora and fauna of the period can hardly be 

 expected to yield any recognisable evidence of fluctuating 



