:tliL PREFATORY REMARKS 



shire we find, in ascending from the tilestones into the mana 

 and sandstones, with concretions of argillaceous limestones 

 (and the same phenomenon re-occurs near Kington, in Here- 

 fordshire), that other species of Pteraspia occur, as well as 

 other species of Cephalaspis, and particularly the C. Lyelli; 

 and thus we are conducted at once into the great formation 

 which, in parts of Scotland, also contains the same species." * 

 Other characteristic organisms, — the large crustacean Pterj- 

 gotus gigas, for example, with its egg-packets, long known by 

 the name of Parka decipienSy — are found associated with 

 the Cephalaspidae, and tell the same story. These facts, the 

 reader will perceive, prove two things : first, that the Ce.- 

 phalaspidae, which include Cephalaspis, Pteraspis, and Auch- 

 enaspis, are unquestionably, as geological discovery at pre- 

 sent stands, the earliest forms of vertebrate life ; secondly, 

 that they and the Pterygoti, <fec., connect Siluria not with the 

 Old Red Sandstones of Cromarty and Caithness, prolific of 

 ganoid fish, but with the Old Red of Forfarshire, where 

 Cephalaspi and Pterygoti are abundant ; consequently regu- 

 lating the succession of the Old Red Sandstone beds. So 

 that the Cephalaspis beds, wherever they occur, as in Forfar- 

 shire, constitute the Lower Old Red ; and those of the Dip 

 teri and Pterichthyi, &c., must move upwards to occupy 

 the middle place. That this arrangement was the true 

 one, the author of the "Foot-prints" suspected before he 

 wrote his " Testimony of the Rocks." In the latter work, 

 in treating of the less known fossil floras of Scotland, after 

 saying that he deemed the evidence of his old reading not ao 



• See Note B, p. 302. 



