191 



NOTES ON THE GLACIAL FORMATION NEAR 

 CHELMSFORD. 



By HORACE VV. MOXCKTON, F.G.S. 

 [Kca.i at the Field Mcctins on July nth, iSgi \ 



npHE sections which we shall see this afternoon' illustrate very well 

 tlie Glacial formation of this part of Essex. It consists of — 



(i) The Great Chalky Boulder Clay. 



(3) The Glacial Sands and Gravel. 



In Norfolk these sands and gravel are underlain by a second 

 Boulder Clay ; but here they rest directly on the London Clay, a 

 marine formation of Eocene age, very much older than the Glacial 

 Period. 



The origin of the Boulder Clay has given rise to a great deal of 

 controversy. At one time it was supposed to be due to a series of 

 great waves raised by hurricanes and storms which swept over the 

 continents, carrying mud and stones of all sorts with them ; but that 

 theory has long been abandoned, and all geologists now, I think, 

 agree that both the Boulder Clay and the materials of which the 

 accompanying sands and gravel are formed were brought into this 

 part of the country during the Glacial Period or Great Ice Age by 

 the agency of ice. There is, however, a great difference of opinion 

 as to the manner in which the ice did the work of transport. Sir 

 Charles Lyell favoured the view that the Boulder Clay was formed of 

 mud and stones melted out of floating ice when nearly the whole of 

 England north of the Thames and Bristol Channel lay submerged 

 beneath the sea ("Antiquity of Man," 4th ed., 1873, p. 273); but 

 many geologists now attribute the transport of the material of which 

 the (ilacial beds are formed to the agency of land-ice, either in the 

 form of a vast sheet which covered a great area, or to more or less 

 local glaciers. The Chalky Boulder Clay is supposed, according to 

 the land-ice theory, to have been pushed or drawn along under the 

 ice, or to have been carried enclosed in the ice and deposited where 

 we now see it when the ice melted ; whilst the sands and gravels are 

 supposed to be due to glacial streams or rivers flowing over, through 



' The sections visited were in the gravel pits at Rainsford End, Writtle Mill, and Rolstons, 

 all in the neighbourhood of Chelmsford and Writile. See the account of the Excursion, 

 fost. 



