22 



POST-TERTIARY ENTOMOSTRACA. 



III. Tlte first great series of fossiliferous Post-Tertiari/ clays, sands, and gravels is 

 characterised by a fauna of a more or less decidedly Arctic character. 



These clays, sands, and gravels are found in the following positions : 

 (1) They exist, in the manner already described, beneath great masses of Boulder 



Clay. 



(2} They are intercalated, as also has been described, with masses of Boulder Clay. 



(3) They either immediately overlie the fossiliferous Boulder Clay or are separated 

 from it only by a thin seam of laminated clay, but are not covered by Boulder Clay. 



(4) They are connected with a series of sands and gravels. 



Examples of Arctic fossiliferous clays beneath the Boulder Clay and intercalated with 

 Boulder Clay have already been discussed ; and we proceed to consider the deposits which 

 are Arctic in character, but are neither situated beneath the Boulder Clay nor intercalated 

 with it. 



IV. A large class of the clays and sands, characterised by an Arctic fauna, in many 

 cases either immediately overlie the unfossiliferous Boulder Clay, or are only separated from 

 it by a than seam of laminated clay, but are not covered by the Boulder Clay itself. 



These beds belong to the period or periods during which an Arctic fauna was most 

 abundantly developed. Whether they consist of clay, sand, or gravel, is, of course, a 

 circumstance of purely local determination, as it is with the marine deposits which are 

 forming at the present day, but since such differences naturally influenced the fauna of 

 which they were the habitat we shall give some details regarding them, as we notice the 

 localities from which our specimens have been obtained. 



As fossihferous deposits they are generally remarkable for the perfect preservation of 

 the various species they contain in situ. At Paisley, e.g., Cyprina Islandica occurs with 

 both valves united and covered with its epidermis; and fragile bivalves like Nucula 

 tenuis, Axinus fexuosus, var. Gouldii, as well as the most delicate Ostracoda, are in a 

 perfect condition. Prom a clay bed near Blairmore, Loch Long, we have gathered 

 numerous specimens of Astarte, including A. borealis, A. sulcata, A. compressa, evidently 

 in their native habitat. In the banks of a freshwater stream near Loch Gilp, a whole 

 bed of Mya Uddevallensis was found, each shell in its natural boring position. 



Beet en Islandicus and Saxicava {Banopad) Norvegica and Mya TJddevallensis have all 

 been collected, in the Kyles of Bute, in the positions in which they lived and died ; the 



