io8 Mr. H. H. Howorth on 



rational explanation of the true succession of so-called glacial 

 deposits in two adjoining counties, much less in two larger 

 geographical areas. Nowhere do we meet with clearer 

 proof of tumultuous and disorderly deposit than in these 

 beds of boulder clay without stratification, and in these 

 local beds of intercalated sand, with their lines of deposit 

 twisted into every conceivable form of curve and eddy. In 

 many places we have no sands at all, in many very large 

 areas we have no boulder clay at all, and yet the acci- 

 dental occurrence of packets of stratified sands or loam, 

 sporadically distributed, is held to prove an interglacial 

 climate. 



Dr. Croll describes the so-called glacial epoch as 

 consisting of a succession of cold and warm periods, 

 the cold periods of one hemisphere coinciding with 

 the warm periods of the other, and vice versa. {Climate 

 and Time, 234.) As Professor Prestwich says, how- 

 ever : — " This would involve an indefinite succession of 

 interglacial periods, but only one definite interglacial 

 period during the glacial epoch is brought forward." Dr. 

 Croll, however, accounts for this on the grounds that " the 

 geological evidences of the cold periods remain in a 

 remarkably perfect state, while the evidences of the warm 

 periods have to a great extent disappeared " (id. 238). " If, 

 however," continues Mr. Prestwich, " one instance would be 

 well preserved, might we not expect other instances to occur 

 in some of the many localities affected ?" I would add that 

 the molars of mammoths, the leg bones of oxen and horses 

 are not more fragile than arctic shells and the leaves of 

 arctic plants. " Dr. Croll estimates the average duration 

 of a warm period at about 10,000 years. Supposing such 

 to have been the case, the phenomena of the glacial series 

 certainly afford no corroboration of the remarkable vicissi- 

 tudes of climate this would infer." (Jour. Geog. Sac, 

 Aug. 1887.) Again Mr. Prestwich says, "It is to be ob- 



