3 PLEISTOCENE MARINE 



containing marine testacea some species of which are extinct 

 or not indigenous to the British Coasts ; 2ndly, the drift 

 or the Boulder formation consisting chiefly of loam, clay 

 and sand, with pebbles and boulders of older rocks, more 

 or less stratified, or sometimes entirely devoid of stratifi- 

 cation. The unstratified portion, to which the term "till" 

 has been commonly applied in Scotland, has abundantly 

 interspersed in it, transported blocks of various degrees of 

 magnitude and from nearly every older formation, such as 

 granite, poryhyry, trap, mica schist, mountain limestone 

 the oolites, green sand, chalk &c. The drift in the north- 

 eastern part of Norfolk overlies the chalk, the crag (at 

 Sherringham) the fluviatile deposits (at Runton Gap) the 

 latter being sometimes intercalated with it (at Mundesley), 

 these freshwater beds being apparently of similar age to 

 those in the valley of the Thames. The drift of Siluria, 

 a loam or clay with fragments of granite and Cambrian 

 rocks, is frequently accompanied with marine shells most 

 of which are identical with species now inhabiting our seas 

 (Kempsey, near Worcester). In Scotland the cb-ift or till 

 reposing on the older rocks appears to be overlied by stra- 

 tified sand and clay, which is sometimes fossiliferous, as at 

 certain points in the estuaries of the Tay, the Forth and 

 Clyde. On the other hand Sir E. I. Murchison has shown 

 that the boulder formation of Russia between St. Peters- 

 burgh and Ai'changel, is superior to strata, containing 

 many species of shells now living in the Arctic sea, and 

 Mr. Lyell mentions that the stratified sand and gravel, 

 near Upsala, with Baltic species of testacea, is overlied by 

 large erratic blocks. From the Arctic character of several 

 shells occuring in the Scottish deposits, it has been inferred 

 that the climate of those latitudes was colder at the period 

 of their deposition than at the present time. Sir R. I. 

 Murchison somewhat dissents fom this opinion as far as 



