REVIEWS, BOOK NOTICES, ETC. 189 



effective, leading to finger-like tongues of shingle to the rear of the 

 spit, lying in the direction of principal wave impact. When high 

 spring tides are accompanied by gales, the crest of the spit may be 

 awash and the impact of the waves may then even promote a land- 

 ward creep of the bank, the mobility of the bank being increased 

 by supersaturation. (2) Percolation, in cases where the bank is 

 steep-sided and the level of high tide above that of the salt-marsh 

 enclosed by the spit. This leads to the erosion of " ravines " by 

 landslip, and the formation of a terrace, by gravitation and detrital 

 faces, on the landward side of the bank, the " ravines " being separ- 

 ated by buttresses of shingle in a quiescent state. (3) Undercutting 

 of the bank on the lee side by tidal or other currents, which some- 

 times plays an important part in regulating the landward creep 

 of the bank. 



Shingle beaches, and especially shingle spits, are shown to belie 

 their appearance both in regard to the soil and to the water they 

 contain. The supply of soil is derived from drift, that from the 

 salt-marshes being considered of more importance than that from 

 the sea, on account of its greater quantity, its richer manurial value, 

 its frequent interstratification with the shingle on the lee side of the 

 bank, and on account of its being the great agency by which certain 

 seeds are sown and placed under favourable conditions for germina- 

 tion. With this is contrasted the enduring sterility of the apposition 

 type of shingle beaches, where contact with tidal waters is denied. 



The water of shingle banks is shown to be astonishingly copious 

 and practically free from salt above the true salt-zone, and, moreover, 

 suffers no diminution during periods of prolonged drought. 



The types of plant habitat on the shingle spit are classified as : — 



(i) The Sea Face, reached by ordinary tides and barren of 

 vegetation. 



(2) The Storm Shelf, with chiefly prostrate species of Atriplex 

 and sometimes Beta maritima. 



(3) The Crest, where wind exposure is a serious check to vegeta- 

 tion, and sometimes distinguished as forming the last stronghold of 

 plants endowed with the capacity of creeping up the shingle from 

 the landward side. 



(4) The Back of the Bank, with its sheltered " ravines," forming 

 the chief region of vegetation, which shows indications of being 

 separable into (i) a vegetation of dormant areas, and (2) that of 

 areas in an unstable condition. 



(5) The Terrace, the gathering-ground of escapes from the salt-marsh. 



(6) The Hooks, which, apart from the terminal hook, are passive 

 and consolidated, and may in certain cases yield distinctive plants 

 as Inula crithmoides or Limonium bitiervosiim. 



In conclusion it may be said that the paper clearly demonstrates 

 the close relation between ecological habitat and the effects of the 

 geological factors of surface change in the shingle spit, and in its 

 method and thoroughness forms an outstanding example of how 

 ecological work should be prosecuted. 



