1911. Stewart. — Flucluations of Sea level. 21 



tell us exactly what was the post-Glacial molluscan fauna. 

 These estuarine clays wherever found have a certain 

 uniformity of characters and assemblage of fossils that 

 entitles them to a distinctive appellation. The terms 

 " Alluvium," " Blue Clay," " Silt." &c., so often used in 

 referring to them seem to me too vague, and I propose to 

 use the term " estuarine clay," which will distinguish this 

 deposit as the contemporary and equivalent of the post- 

 Glacial raised beaches. In the geology of recent times 

 these clays hold a place corresponding to that of the raised 

 beaches that have been so much discussed of late. Owing, 

 however, to the fact that the clay deposits require the 

 investigator to turn himself into a navvy for the time 

 being, and to maintain a special outfit for the purpose of 

 working ankle deep in unsavoury mud, they have not been 

 so well examined as the raised beaches ; further, no matter 

 how willing one may be, it is only on rare occasions that 

 good opportunities offer for their examination. 



We in Belfast may take credit, however, for our share 

 in this line of research. Several members of the Natural 

 History Society have from time to time paid attention to 

 the subject, and the late Messrs. Thompson and Hyndman 

 left behind them collections of the shells. Up to the present 

 time, however, no British geologist has done so much in 

 this department as a member of the Belfast Naturalists' 

 Field Club. I refer to Mr., now the Rev. Dr. Grainger, 

 whose list of the Belfast clay shells is the most complete 

 list of estuarine clay fossils yet published, and as such is 

 always quoted by the writers on this particular branch of 

 geology. The hsts I refer to will be found in the reports 

 of the British Association,^ and in the transactions of 

 Dublin University Zoological Society," The estuarine clay 

 beds present better opportunities for the study of recent 

 geological history than do the raised beaches. We find in 

 them deposits of considerable thickness which have been 

 continuously laid down. The order of succession is unbroken, 

 and such changes in the fauna as have occurred may be 



' Report for 1852, Sections, pp. 43-46, 74-75. 



2 Proc. Dublin Univ. Zool. and Bot. Assoc, i., 202-222. 1859. 



