POST-TERTIARY FOSSILIFEROUS DEPOSITS. 



11 



§ II. VARIETIES OF EOSSILIFEROUS DEPOSITS, NOT BEING BOULDER- 

 CLAYS. 



Necessary as it is to distinguish the so-called " Boulder Clays " from each other, it 

 is equally necessary to note the differences existing between those numerous Post-tertiary 

 fossiliferous deposits of Scotland which cannot under any circumstances be described as 

 Boulder Clays, and in the larger number of which Ostracoda occur in more or less abundance. 



In the earlier researches into the Post-tertiary beds of Scotland two superficial deposits 

 alone were noted. The lowest was vaguely termed " Till, a stiff unstratified clay mixed 

 with boulders," while the upper was described as brick or finely laminated clay overlain 

 by sand and gravel. The whole of the fossils fonnd were classed together and catalogued 

 by Mr. Smith of Jordan Hill, in the first catalogue ever issued,^ as belonging to the 

 " Newer Pliocene deposits in the British Islands." 



As Mr. Smith's investigations proceeded he discovered that he had confounded two 

 distinct sets of beds, and that there were in the elevated marine beds of sand, gravel, and 

 clay, which cover the older formations, at least two deposits differing in climate and 

 fauna, and separated by wide intervals of time.^ He discriminated the " glacial deposits" 

 of Great Britain and Ireland from the " raised beaches," and a Glacial Epoch was added 

 to the geological record. 



Mr. Smith published a* second catalogue in which he confined himself to the marine 

 Testacea, including Cirripedia, Annelida, and Foraminifera " — Ostracoda had not then 

 been detected — of the " glacial deposits."'^ This catalogue, however, presents many 

 difficulties. Apart from the fact that there is a very perplexing employment of 

 synonyms, the original specimens from which several " new species " were described have 

 not been preserved, so that it is impossible to decide whether some of them may not 

 have been identical with the varieties of modern conchologists, and many of the localities 

 are far too vaguely specified for identification. 



The simple distinction between " raised beaches " and " glacial deposits " does not at 

 all cover the whole ground occupied by the fossiliferous beds in question. 



1 'Transactions of the Wernerian Society.' 1839. 



2 ' Reseaixhes in Newer Pliocene and Post-tertiary Geology.' By James Smith, F.R.S. Glasgow t 

 John Gray. 18G2. 



^ Ibid., p. 46. In connection with tbis department of Scotch Geology, the name of Mr. Smith ought 

 always to he honourably remembered, and the results of his researches acknowledged. His collected papers 

 indicate the successive steps which led to his great discovery, and constitute a chnpter of great value in the 

 history of Post-tertiary geology. 



