1893. EFFECT OF GLACIAL PERIOD. 263 



on the coasts of Portugal ; and he adds : " For a short space, and 

 but a very short space, the two faunas intermingle." ' 



Take, again, certain parts of the Atlantic Ocean at the present 

 day. A mingling of arctic with temperate forms of life must occur 

 among the deposits there accumulating by means of currents flowing 

 south from colder regions, and the Gulf Stream flowing north from 

 temperate regions. 



A similar mixture must occur in the seas north of Siberia, since 

 the great rivers flowing from the far South will carry temperate forms 

 of life to be interbedded with the natives of those icy seas. 



An interesting example of the mingling of temperate and arctic 

 forms is recorded from the New Siberian Islands. Here in one 

 deposit were found bones of a long-haired variety of the tiger, along 

 with those of the musk ox, mammoth, etc.^ 



Leaving, however, the doubtful evidence of the so-called '' inter- 

 glacial " beds, are there any indications of survival in undoubted 

 Glacial deposits ? 



In the Glacial fresh-water beds which occur at the base of the 

 Glacial series in Norfolk, Salix polaris and Betida nana occur along with 

 Planorhis complanahis, Succinea piitris, and S. oblonga. -The first of these 

 species of mollusca occurs everywhere in England, Wales, and 

 Ireland ; the second is fairly common, and the third rare and local 

 at the present day. Thus the cold which brought Salix polaris did not 

 drive away these temperate forms of mollusca. 



In the Boulder Clay of Norfolk, again, the following species are 

 recorded : — Cardium ediile, Tellina lata/'- Cypvina islandica, Littorma 

 littorea, Mya arenaria, Pleurotoma turvicula,'''- Pholas crispata. With the 

 exception of those marked thus ''■■, all occur in the succeeding Glacial 

 gravel ; they all, without exception, occur in the preceding Pliocene, 

 while only Tellina lata is extinct as a British shell. 



Cardium ediile is now common round our coasts ; Cyprina islandica 

 ranges as far south as Boulonnais and Cherbourg ; Mya arenaria 

 occurring in South Greenland, ranges as far south as Rochelle ; 

 Pholas crispata extends to the North of France; Littorina littorea ranges 

 between Greenland and Lisbon ; Pleurotonia tiirrictda occurs on every 

 part of the British coasts. 



As regards Mammalia, Elephas primigenius is recorded from the 

 Boulder Clay of the same district, and doubtfully from the Glacial 

 gravel ; Cerviis elaphus is doubtfully recorded from the Boulder Clay. 



When we turn to the West Coast of England we find in the 

 organic remains of the Boulder Clay still stronger indications of the 

 possibility of survival. Thus the great majority of shells found in 

 the Boulder Clay of Liverpool are such as are living in British seas 

 to-day ; only two, Astarte borealis and Saxicava rugosa, are distinctly 



"^ Mem. Gcol. Surv., vol. i , p. 377. 



^ Mem. Acad. Imp. Sci. St. Pitersbourg, vo\. xl., no. i. Referred to in "Notes 

 and Comments," Natural Science, March, 1893, p. 170. 



