626 REPORT — 1901. 



Lanarkshire strata, the nearest related genus to Cephalaspis being Ateleaspis, 

 which, however, represents a distinct family. 



The g-roup of sandstones, conglomerates, shales, and mudstones that form the 

 passage-beds between the Ludlow rocks and the Lower Old Red Sandstone in 

 Lanarkshire are now regarded as the equivalents of the Downtonian strata in 

 Shropshire, and are linked with the Silurian system. The mudstones of this 

 group, containing the new fish fauna, likewise yield ostracods, phyllocarid crus- 

 taceans, and eurypterids— forms which connect these beds with the underlying 

 Ludlow rocks. The band of greywacke-conglomerate, that extends from the 

 Pentland Hills into Ayrshire, composed largely of pebbles derived from the 

 Silurian tableland, is now taken as the base line of the Lower Old Red Sandstone 

 on the south side of the great midland valley of Scotland. 



The period under review has been marked by important additions to our know- 

 ledge of the Old Red Sandstone formation. In 1878 appeared a valuable mono- 

 graph by Sir Archibald Geikie on ' The Old Red Sandstone of Western Europe,' ' 

 by far the most important treatise on this subject since the publication of Hugh 

 Miller's classic work published in 1S41. Following up the view maintained by 

 Fleming, God win- Austen, and Ramsay, that the deposits of this formation were 

 laid down in lakes or inland seas, he defined the geographical areas of the various 

 basins in the British area, giving to each a local name. He gave an outline of the 

 development of the rocks north of the Grampians, in Caithness, Orkney, and 

 Shetland. He advanced an ingenious argument in favour of correlating the 

 Caithness flagstone series (middle division, Murchison) with the Lower Old Red 

 Sandstone south of the Grampians. He contended that ' the admitted paltEonto- 

 logical distinctions between the two areas are probably not greater than the 

 striking lithological differences between the strata would account for, or than the 

 contrast between the ichthyic faunas of adjacent but disconnected water basins at 

 the present time.' Sir A. Geikie further gave a table showing the vertical range 

 of the known fossils of the Caithness series from data partly supplied by the late 

 Mr. C. Peach. 



During the last quarter of a century Dr. Traquair has made a special study of 

 the ichthyology of the Old Red Sandstone and Carboniferous strata of Scotland, 

 which has enabled him to throw much light on the distribution of fossil fishes in 

 these rocks and on their value for the purpose of correlation. His researches 

 show that the fish fauna of the formation south of the Grampians resembles that 

 of the Lower Oid Red Sandstone of the West of England and adjoining part of 

 Wales in the abundance of specimens of Cephalasjns, the common species in 

 Forfarshire (C. Li/elli, Ag.) being also indistinguishable from that in the Hereford- 

 shire beds. Pteraspis occurs in both regions, though of different species. Of 

 Acanthodians Pare.rus recurviis, Ag.. occurs in both, together with Climatius 

 (C. ornatus, Ag.). The abundance of Cephalaspis (C. Campbelltonensis, Whit., 

 C. Jexi, Traq.) and of Clinudius spines is characteristic of the Lower Devonian 

 rocks of Canada. 



The Old Red Sandstone of Lome has recently yielded organic remains, akin to 

 those found in Forfarshire, south of the Grampians, viz., Cephalaspis Lornensis 

 (Traq.), two species of myriapods {Campecaris Fovfarensis and a .species of 

 Archidesmus')." 



In the deposits of Lake Orcadie, north of the Grampians, quite a different fish 

 fauna from that of Forfarshire appears. Dr. Traquair has noted that there are no 

 species common to the two areas, and only two genera, viz., Mesacanthiis and 

 Cephalaspis. The latter genus is, however, represented in Caithness only by a 

 single specimen of a species (C. magmfica, Traq.) different from any found else- 

 where. It might here be observed that Cephalaspis is represented also in the 

 Upper Devonian rocks of Canada by a single specimen of a peculiar species 

 (C. laticeps, Traq.), and hence Dr. Traquair has shown that, though CephalasjJtsia 

 most abundant in the Lower Devonian, it extends also into the upper division of 



' Trans. Roy. Snc, Edin., vol. sxviii. p. 345. 



- Summary of Progress,] Geological Survey, 1897, p. 83. 



