2.38 



TriF, MENDTPS I A GEOLOUTCAL HEVERIE. 



existence as a range of hills, the Old Eecl Sandstone rocks 

 which to-day form their heart, were deposited near the 

 margin of a sea which lay over what is now Devon and 

 Cornwall, spreading thence eastwards through northern 

 Franco and Belgium. Their deposition marked the close 

 of a long era, the Devonian of geologists, during which the 

 northern parts of our islands lay within the coast-line of a 

 great continent stretching awny northwards and perhaps 

 westwards, nobody knows how far. In the early part of 

 this period tliore lay within the bounds of this continent a 

 series of groat Scottish lakes, tenanted by strange typos 

 of old-world creatures. Of the armoured fishes, repre- 

 sented to-day by such scattered forms as the Polypterus of 

 the Nile, the Calamoichthys of Old Calabar, and the Alli- 

 gator-gar of the American lakes, there were many and 

 various representatives, some with sharp, thornlike fin- 

 spines ; others with enamelled, bony helmet ; aiul many 

 with overlapping smooth or wrinkled scales. With them 

 were the quaint Eurypterids, welcomed by the author of 

 the "Vestiges" as crustaceans, struggling not unsuccess- 

 fully to become fishes ; and welcomed again by pious 

 quarrymen, who regarded their ventral plates, or fused 

 appendages, as the fossil wings of cherubim. 



One of the Scotch lakes in which these creatures lived, 

 Ijake Orcadie (see Ma]) 1 *), lay to the north of the Scottish 

 Highlands, reaching to the Orkney and Shetland Isles, 



* The Scotch lakes were named and defined by Dr. A. Goikie. Mr. 

 .Jvikes-Brownc, however, questions ttio distinctness of all these basins. 

 The map is modified from that given by Prof. Hull in his "Physical 

 History of the British Isles." The reader is, however, earnestly warned 

 in regard to this and succeeding maps, that the boundaries laid down in 

 them cannot be fixed with any approach to certainty. They are aids to 

 the imagination, and serve to give the history of the past an air of 

 reality; but they are constantly liable to modification by further and 



