PALEOZOIC TIME — DEVONIAN. 



623 



979. 



The Old Eed sandstone is the rock of all the areas excepting that of 

 Devon and Cornwall. It consists of red, purplish, and brown sandstones, 

 coarse and fine, passing to a conglomerate and also to bituminous flags. It 

 shows by its coarse and varying- features, by the absence of fossiliferous beds 

 bearing shells, corals, and other invertebrate remains, and by the presence 

 here and there of relics of Fishes and Eurypterids, that its origin was much 

 Hke that of the Catskill Eed sandstone of eastern America — a roughly 

 made sea-border formation, in waters that suffered in purity from the contri- 

 butions of streams from the bordering hills. The American Devonian has 

 abundant life beyond the Catskill sandstone area ; and in the British seas 

 the beds of Devon are as prolific as the Chemung, Hamilton, and Corniferous 

 of eastern America. 



The Old Red sandstone of Scotland (called Old Eed in contrast with the 

 New Bed or Triassic) is reported to have the extraordinary thickness of 

 10,000 to 16,000 feet. It is 

 divided into an Upper and 

 Lower division, by a plane 

 of unc onf or m ability above the 

 level of the Caithness flags 

 (A. Geikie). Besides sand- 

 stones the central basin of 

 Scotland includes a great 

 thickness (6000 feet) of igne- 

 ous rocks — f elsyte and f el- 

 syte porphyry, doleryte and 

 other kinds ; now forming, as 

 Geikie states, chains of hills, 

 as in the Pentland, Orchir and 

 Sidlaw ranges. They occur 

 interstratified with the ordi- 

 nary beds, several thousand 

 feet above the base of the 

 Devonian, and indicate a long 

 period of ejections. The ba- 

 sins of the Cheviot Hills and 

 of Lome also had their vol- 

 canic ejections. 



The Old Eed sandstone is 

 remarkable for its Eurypterids. 

 A Pterygotus is represented in 



Eig. 979, P. Anglicus, which has a length of six feet — more than three 

 times that of any Crustacean now living. Other common genera are 

 Eurypterus and Stylonurus. An Ostracoid, Estlieria, is abundant in some 

 places. A gigantic Isopod Crustacean, the Prcearcturus, has been described 

 by Woodward (1870) from the Old Eed sandstone of Herefordshire. 



EtTEYPTERiD. — Fig. 979, Pterygotus Anglicus; a, eye; 

 /, appendages ; 1 to 18, numbering of segments. 



