QUATERNARY DEPOSITS OF BRITISH ISLES — BROOKS. 313 



The phanerogam flora indicates conditions only found to-day with- 

 in the Arctic Circle, but less rigorous than those at Spitzbergen. 



The sequence of stages in the* Thames Valley may accordingly 

 be made out as follows: 



1. Maximum glaciation of eastern England — Chalky bowlder clay of 

 Finchley. 

 . 2. Highest and 100-foot terraces of Thames with Corhicula fluminalis 

 and Paludina diluviana. Chellean and Acheuliau correspond to 

 the marine gravels of March and Holderness. 



3. Period of erosion. 



4. Middle terrace, temperate at first, but becoming cold later. Acheulian 



Mousterian. 



5. Cold period. Arctic beds of Lea A-'alley ; " warp and trail." 



6. Erosion, late Mousterian period ; no evidence as to climate. 



7. Low terrace formed. Probably cold. Solutrean to Magdalenian. 



The correlation of the Quaternary stages of eastern England and 

 the Thames Valley with those of Holland and north Germany is very 

 clear, if ordinary stratigraphical and paleontological methods are 

 employed. The Cromer forest bed and the Tegelen plant beds must 

 be equivalents on the grounds of both stratigraphy and flora. Each 

 was immediately followed by the maximum glaciation of the district. 

 The close of the glaciation was marked in each case by a submergence, 

 characterized in the north by marine formations (Holderness gravels, 

 Eem beds) and in the south by river terraces (130-foot terrace, chief 

 terrace). The characteristic Mollusca of these beds on both sides 

 of the North Sea are, first, Corhicula fluminalis ,' second, Paludina 

 diluviana. Finally, we have in both east England and Holland a 

 minor glaciation, associated with the Mousterian industry, and with 

 the middle terrace group of the rivers. 



SOUTH COAST. 



South of the Thames Valley no bowlder clay is known, but there 

 are other evidences of a severe climate in the coombe rock or "head" 

 and in the presence of large erratic bowlders. 



The section at Brighton was described by Mantell in 1833 (81) : 



a. Elephant bed (coombe rock). 



b. Ancient shingle (witli erratics). 



c. Ancient sand. 



d. Base of cliffs, of chalk rock. 



According to Mantell, the junction of the coombe rock with the 

 shingle was marked by a layer of shells, including Cardiv/m edule, 

 Mytilus edulis^ Litorlna litorea^ and Purpura laq)lllu$.^ but in 1914 this 

 was not visible; instead the junction was marked by a layer of chalk 

 pebbles. A few hours' search in the shingle beds yielded a large 

 number of erratics, many of them gray and pink granites of north- 



