598 ox THE EEEATICS IX THE BOITLDEP.-CLAT OF CHESHERE 



in the Boulder-clay near Belfast have chips and flakes broken oif, 

 and the resulting angles crushed in a similar manner to some in the 

 Boiolder-clay of Cheshire and Lancashire. The most probable 

 explanation of the separation of the chips and flakes is that the 

 liints, \rhilst enveloped in glaciers, passed over the platforms formed 

 of layers of flints so constantly interstratified with the Chalk or 

 White Limestone of Co. Antrim. 



The peculiar instances of ■weathering which rocks of difl'erent 

 kinds have undergone prior to their deposition in the Boulder-clay 

 appear to have escaped notice almost entirely, with the exception of 

 blocks of disintegrated granite and trap ; these are too conspicuous 

 to be overlooked. The consideration of all these phenomena tends 

 to prove that, during the glacial period, though the climate was 

 always of an arctic character, with perennial snow resting on the 

 ground, there were frequent variations in the severity of the 

 seasons — that a less amount of snow fell during one series of years 

 than during another, so that for a considerable time glaciers receded, 

 leaving the contents of moraines exposed to vicissitudes of the 

 weather, to repeated successions of frost and thaw, probably re- 

 curring daily during several months in the year. Again they in- 

 creased in size and carried forward the accumulations as an integral 

 part of their volume, so that they eventually reached the sea, and 

 icebergs were formed, "forced ofp from their parent glaciers by the 

 buoyant action of the sea " and floated away. They cannot be con- 

 sidered to represent an interglacial period such as the examination 

 of certain deposits in Scotland and elsewhere is supposed to indicate ; 

 for these weathered erratics are found in all situations in the Boulder- 

 clay. The changes in climate which took place appear to have been 

 not unlike those which occur in Greenland, where it is recorded that 

 the glaciers have been observed to successiveh' recede and advance to 

 the extent of several hundred yards *. In some respects they may be 

 compared to changes of climate in our own country, where some 

 winters are mild and others severe, some remarkable for abundance 

 of rain or snow, others for frost and fine weather. 



Discussion. 



Dr. EvAxs thought the observations of Dr. Eicketts were of very 

 great interest, whatever interpretation was put upon them. 



Dr. HiCES asked if it were not possible that some of the changes 

 indicated were due to the percolation of water through the sandy 

 boulder-clays. 



The AuTHOE, in reply, said the evidence was entirely in favour of 

 the decomposition having taken place before the imbedding of the 

 fragments. 



* " On the Ice-fjords of North Greenland," by Amund Helland, of 

 Christiania (Quart. Journ. Geol. Soc. vol. xxxiii. p. 154). 



