Dr. Croll's Theory of Glacial aiid Warm Periods. 103 



are computed there were five periods during which the 

 eccentricity was as great or greater than during the glacial 

 epoch proper ; so that taking the geological time at the 

 hundred million years, at which he estimates it, there should 

 have been in all probability some 165 such periods of 

 cold. With the exception of the permian, which is still 

 pendente lite, where is there any evidence of any such cold 

 periods?" 



In regard to the evidence of the so-called miocene beds 

 quoted by Dr. Croll, from North Italy, Mr. Prestwich says : 

 " The fact of the miocene date of the beds in question has 

 never since been confirmed ; all the later evidence tends to 

 show that it was not until towards the close of the pliocene 

 period that glacial conditions set in." 



"For the pliocene period Dr. Croll relies on another Alpine 

 case, the coarse conglomerates with some enormous blocks 

 forming the Flysch. But this was a period of Alpine 

 disturbance and change, when, though the rocks may have 

 been rent and worn down in the mountain area, the marine 

 life at a short distance gives evident indication of a high 

 general temperature. Nummulites then abounded in the 

 surrounding seas, together with echinoderms of a decidedly 

 tropical aspect. 



" The case for the chalk is still weaker, for the very few 

 and exceptional foreign rock boulders that have been found 

 in it are of small size, such as might have been carried in the 

 roots of trees, or by sea weeds, or possibly by small winter 

 ice rafts from the mountains of Scandinavia or the Ardennes, 

 while all the life of the Cretaceous sea is strictly that of 

 temperate, if not of warm latitudes. The small pebbles 

 may have been carried by the large marine reptiles." 



Speaking of the mass of granite rock found by Godwin 

 Austin imbedded in chalk at Croydon, Mr. J. Gunn says, 

 " it exhibits no more than the washing of the land by floods, 

 or inroads of the sea, .... such masses arc rounded 



