Oh. XXVL] STRATA OF SOUTH DEVON. 535 



Huxley's Crossopterygii is the Pterichthys, of which five species 

 have been found in the middle division of the Old Red of Scotland. 

 Some writers have compared their shelly covering to that of Crusta- 

 ceans, with which, however, they have no real affinity. The wing- 

 like appendages, whence the genus is named, were first supposed by 

 Hugh Miller to be paddles, like those of the turtle ; and there can 

 now be no doubt that they do really correspond with the pectoral 

 fins. Professor Huxley, when speaking of the allied genus Coccosteus, 

 has speculated on its relationship with the Siluridee, a large family of 

 living Teleosteans, the bony shields covering the roof of the cranium 

 in Coccosteus being compared by him with those which cover the 

 head and anterior part of the body of certain Siluroids, more par- 

 ticularly those belonging to the genus Clarias. 



South Devon and Cornwall. — Term Devonian. — -A great step was 

 made in the classification of the slaty and calciferous strata of South 

 Devon and Cornwall in 1837, when a large portion of the beds, pre- 

 viously referred to the " transition " or Silurian series, were found to 

 belong in reality to the period of the Old Red Sandstone. For this 

 reform we are indebted to the labors of Professor Sedgwick and Sir 

 R. Murchison, assisted by a suggestion of Mr. Lonsdale, who, in 1837, 

 after examining the South Devonshire fossils, perceived that some of 

 them agreed with those of the Carboniferous group, others with those 

 of the Silurian, while many could not be assigned to either system, 

 the whole taken together exhibiting a peculiar type, but of intermediate 

 character between the older and newer groups alluded to. But these 

 palseontological observations alone would not have enabled us to assign, 

 with accuracy, the true place in the geological series of these slate- 

 rocks and limestones of South Devon, had not Messrs. Sedgwick and 

 Murchison, in 1836 and 1837, discovered that the culmiferous or 

 anthracitic shales of North Devon belonged to the Coal, and not, as 

 preceding observers had imagined, to the " transition" period. 



As the strata of South Devon here alluded to are far richer in 

 organic remains than the red sandstones of contemporaneous date in 

 Herefordshire and Scotland, the new name of the " Devonian system " 

 was proposed as a substitute for that of Old Red Sandstone. 



The link supplied by the whole assemblage of imbedded fossils, 

 connecting as it does the palaeontology of the Silurian and Carbon- 

 iferous groups, is one of the highest interest, and equally striking 

 whether we regard the genera of the corals or of the shells. The 

 species are mostly distinct except in the upper group. 



The rocks of this group in South Devon consist, in great part, of 

 green chloritic slates, alternating with large quartzose slates and sand- 

 stones. Here and there calcareous slates are interstratified with blue 

 crystalline limestone, and in some divisions conglomerates, passing 

 into red sandstone. But the whole series is much altered and dis- 

 turbed by the intrusion of the granite of Dartmoor and other igneous 

 rocks. 



