NOTES OX PALEOZOIC CRUSTACEANS 105 



basins, has designated^ some of the areas in terms of recent 

 topography as " the Welsh lake ", " Lake Caledonia " and " Lake 

 Orcadie ''. Welsh lake lies in southern Britain and extends 

 from Shropshire into South Wales. 



Here the uppermost parts of the Silurian system graduate into 

 red strata, not less than 10,000 feet thick, which in turn pass up 

 conformably into the base of the Carboniferous. 



In some of the higher parts . . . Serpula and C o n- 

 n 1 a r i a occur; but these are exceptional cases and point to the 

 advent of the Carboniferous marine fauna, which doubtless ex- 

 isted outside the British area before it spread over the site of 

 the Old Red sandstone basins. 



Lake Caledonia lies in the southern counties of Scotland. 



Lake Orcadie ^' lies on the north side of the Highlands, but only 

 a portion of it comes within the present area of Scotland. It 

 skirts the slopes of the mountains along the Moray firth and east 

 of Ross and Sutherland and stretches through Caithness and the 

 Orkney islands as far as the south of the Shetland group. It 

 may possibly have been at one time continued as far as the 

 Sognefjord and Dalsfjord in Xorway, where red conglomerates 

 like those of the north of Scotland occur. There is even reason 

 to infer that it may have ranged eastward into Russia, for some 

 of its most characteristic organisms are found also among the 

 Devonian strata of that country. 



The Old Red sandstone of the northern basin (Lake Orcadie) 

 is typically developed in Caithness, where it consists chiefly 

 of the well-known dark gray, bituminous and calcareous flag- 

 stones of commerce. It rests unconformably on metamorphosed 

 Lower Silurian schists and must have been deposited on the 

 very uneven bottom of a sinking basin, seeing that occasionally 

 even some of the higher platforms are found resting against 

 the schists and granites . . . The total depth of the series 

 in Caithness has been estimated at upwards of 16,000 

 feet . . . Somewhere about 60 species of fishes have been 

 obtained from the Old Red sandstone of the north of Scotland. 

 Among these the genera Acanthodes, Asterolepis, 



^Roy. soc. Edin. Trans. 1879. v. 28. 



