294 R. D. Oldham — On Homotaxis and Contemporaneity . 



finally, and we are consequently compelled to search for some other 

 evidence which will enable us to say, in some cases at any rate, that 

 the beds are or are not strictly contemporaneous in their origin. 

 One possible means would be the traces left by a period of cold 

 similar to the well-known " Glacial period " of Post-Tertiary times. 

 That there was such a period during which an arctic climate pene- 

 trated into temperate regions has been amply proved, and we may, 

 I think, safely assume that this " Glacial " period of cold was con- 

 temporaneous in both hemispheres ; for, whatever may have been 

 the cause of the colder climate which prevailed during that period, 

 it must have affected both hemispheres in the same manner at the 

 same time. 



I am not overlooking the fact that the most probable theory of the 

 Glacial period, that of Dr. Croll, necessitates the glaciation of one 

 hemisphere contemporaneously with the prevalence of a mild climate 

 in the other ; but if we take the Glacial period as a whole, which 

 includes all the minor glacial and interglacial periods, we may say 

 that the Post-Tertiary deposits which show signs of a colder climate 

 than now prevails are of. contemporaneous origin, wherever they 

 may be found. By this I must not be understood to mean that any 

 one particular bed in one place can be declared to be contempora- 

 neous with a definite bed anywhere else, but that the series as a 

 whole were of contemporaneous origin, though the actual limits may 

 not have been the same in both cases. 



If we can prove that similar Glacial epochs have occurred during 

 the sedimentary period, using the term to denote that period of the 

 Earth's history which is represented by the sequence of sedimentary 

 formations, we shall have an important check on the palasontological 

 timepiece, by which we can determine whether it is fast or slow. To 

 prove this it will not be sufficient merely to point out that evidences 

 of glacial action have been detected by various observers in strata of 

 various ages, and in latitudes lower than those in which icebergs are 

 met with at the present day ; but if it can be shown that, in several 

 widely-separated regions, and in strata which can on independent 

 grounds be shown to be, at least, approximately homotaxial, there 

 are to be found extensive indications of glacial action, which are not 

 seen in the beds above or below, we may safely and fairly conclude 

 that they all belong to a single Glacial epoch comparable to that 

 of Post-Tertiary times. 



For this purpose I shall take that Glacial period represented by 

 the Talchir beds of India, the Ecca beds of Africa, and certain beds 

 in Australia likewise of glacial origin. I choose this particular in- 

 stance because the details are more familiar to me than any other, 

 and moreover I shall be able to place before the readers of this 

 Magazine some recent additions to our knowledge of the geology of 

 these countries. 



It must be well known that there have been serious differences of 

 opinion regarding the age of the Indian and Australian Coal-measures, 

 and that this difference has practically been between the field geolo- 

 gists on the one hand and the palasobotanists on the other. The former 



