Marine Acciwiulations in Largo Bay, and Portrush. 291 



than subaerial, I am reluctantly compelled to differ from him 

 in referring to it as a " raised beach." 



Useful as the words " raised beach " may be as a geological 

 term, they are not sufficiently explicit in a palseontological 

 sense, because beach faunas have their own peculiarities 

 differing in many respects from faunas accumulated under 

 other conditions. 



The fauna of a raised beach depends upon the nature of 

 the beach itself. If a fiat sandy shore, the sands and shells 

 will be swept up beyond tide mark into dunes ; if bounded by 

 cliffs or a rocky shore, the organisms are usually much broken 

 or swept off by recurring tides. A true beach fauna is 

 confined to comparatively few species, usually Littorina, 

 Alytilus, and Carclium (species that can live out of water for 

 hours), except towards the verge of extremely low tides. 



From the abundance of species, state of preservation, and 

 mode of presentation, the Largo Bay accumulation appears 

 to be a current-bedded sand-bank formed in the laminarian 

 zone, the remains being proper to that horizon, heaped up 

 between Kincraig on the east and Kilconquhar on the north. 



One of the most important features in this deposit are the 

 number of mollusca (nearly 13 per cent.) not found living in 

 the Firth of Forth at the present time, taking the lists ^ of 

 Messrs Leslie and Herdman as a standard to go by. Further 

 research will probably reduce the number of missing species, 

 but it is certainly desirable to call notice to these, and to the 

 Foraminifera, of which nearly 50 per cent, do not occur in 

 the above lists. 



This may indicate a considerable lapse of time since the 

 formation of the deposit, but does not carry it back to the 

 age of the Clyde beds, containing Tellina calcarca and Lcda 

 permola, whose nearest habitat is Fair Isle and the Faroes — 

 deposits usually called raised beaches, but are more properly 

 raised sea-bottoms. 



The lists are still incomplete, as a further examination 

 shows the existence of other organisms — Entomostraca and 

 other things, — of which a list will be afforded at a later 

 period when identified. 



1 The Invertebrate Fauna of the Firth of Forth. Edinburgh, 1881. 

 Reprinted from Proc. Roy. Phys. Soc. Edin., vol. xi., pp. 68, 201, 2(JS. 



