108 



leaves of marsh plants, and some shells and mammalia. Each was preceded 

 and followed by a period of greater cold. The antecedence of a colder 

 climate is proved by the arctic character of a large proportion of the shells of 

 living species, included in the marine strata of Chillesford, near Ipswich, and 

 that the forest bed of Cromer was followed by an era of severe cold, is shewn 

 by the fact that it underlies the great mass of glacial drift, in part unstra- 

 tified, and containing boulders and angular blocks transported from great 

 distances, and some of them exhibiting pohshed and striated surfaces. 

 With regard to the Diimten bed, we have abundant evidence of two glacial 

 periods in the Alps, during the first of which the glaciers attained colossal 

 dimensions. After these had retreated for a time, they advanced again, but 

 on a smaller scale, though still vastly exceeding in size the largest Swiss 

 glacier, of our day. The interval of milder weather, marked by the 

 decrease of snow and ice in the Alps, has been called by Prof. Heer the 

 Inter-Grlacial Period, which must have been of considerable dui-ation, for it 

 gave time for the accumulation of dense beds of lignite, like those at 

 Diimten and other localities near Zurich. During this intercalated series 

 of warm seasons, the climate is supposed by Heer to have closely resembled 

 that now experienced in Switzerland. He infers this from the fossil flora 

 of the lignite, especially from the cones of the Scotch and Spruce firs, and 

 the leaves of the ash and yew — all of living species — as well as from the 

 seeds of certain marsh plants. 



Sir Charles Lyell further says : — 

 We are by no means suSiciently advanced in our interpretations of the 

 monuments of the Glacial Epoch, and of the long succession of events which 

 mark its histoiy, to be able to affirm that the Inter- glacial periods of 

 Diimten and Cromer, above mentioned, were contemporaneous, but they 

 both oi them alike demonstrate that there were osciLLations of temperature 

 in the course of that long epoch of cold. 



In Messrs. Wood and Romes' valuable paper in the Quarterly 

 Journal for May, 1858, on the Glacial and Post-glacial Sti'ucture 

 of Lincolnshire and South-east Yorkshire, thei*e is an account 

 of a forest bed at Hull, and Grimsby, and of which I have given 

 the section of the beds at the HuU Docks. They remark : — 



" At Hull the dock borings showed this forest to be now from 20 to 37 feet 

 below high water mark of ordinary spring tides, the whole of that depth 

 being occupied by the silt with moUusca and salt water. The boiings for 

 the Grimsby Docks disclosed the same forest bed at still greater depths, 

 varjdng from 35 to 52 feet below high water of ordinarj' spring tides, and 

 everywhere covered with silt and salt water. From the Grimsby borings 

 (which were more than 100 in number, and principally carried to depths of 



