DISTINCT GLACIAL EPOCHS. 69 



warm or long to be regarded as an interglacial epoch.' Cal- 

 careous concretions, like those of the loess, would possess a like 

 significance, in like relations. While in themselves these inor- 

 ganic products of a time of ice recession might fail to be con- 

 clusive of separate ice epochs, they might have much corrobo- 

 rative significance when associated with other phenomena. An 

 inter-till iron ore bed, associated with a forest bed which indi- 

 cated a warm climate, would be most significant. 



The absence of knowledge of ore beds between sheets of till, 

 and the absence from an upper bed of till of concretions of iron and 

 lime carbonate formed during a recession of the ice, would be 

 no proof that interglacial epochs did not occur. These products 

 were probably formed in relatively few localities. They stood 

 good chance of destruction at the hands of the returning ice, and 

 they may exist, where they have not been discovered, or where 

 their significance has not been understood. Their absence is at 

 best no more than negative evidence. 



(4) Beds of Mari?ie and Lacustrine Ongi?i. If between beds 

 of glacial drift there be found beds of lacustrine or of marine 

 origin, such beds would indicate a recession of the ice during 

 their time of deposition. Their position would be a minimum 

 measure of ice recession. If such lacustrine beds contain 

 organic remains, they will bear testimony concerning the climatic 

 conditions which existed where they occur, at the time of their 

 deposition. If the fossils in such beds denote a temperate cli- 

 mate, or a climate as mild as that of the present day in the same 

 region, the ice must have receded so far to the northward as, in 

 our judgment, to constitute its re-advance a distinct ice epoch. 

 This line of argument may be even stronger than that drawn from 

 remains of terrestrial life, since the ice would probably affect the 

 temperature of the sea to greater distances than that of the land, 

 and affect it to a greater degree within a given distance. The 

 argument becomes stronger the further north the inter-drift 

 marine and lacustrine deposits occur, since the ice must always 



'This point concerning iron nodules was suggested to the writer by Mr. W. J. 

 McGee. 



