SILURIAN SYSTEM 177 



Salopian. In tin- main l>elt the Gala Group is succeeded by 

 tin Kiccarton Beds, a series of conglomerates, grits, mudstones, and 

 shales from 1000 to 1500 feet thick, and containing Oyrtograptug 

 Mi'irfiisoni, Monograptus vomerinus, and M. priodon. At Raeberry 

 near Kirkcudbright there are still higher beds, consisting of green 

 marls with limestone nodules, which are either highest Wenlock or 

 possibly Lower Ludlow. These are 700 feet thick. 



In the Girvan area the representatives of the Wenlock Beds 

 consist largely of unfossiliferous flagstones, and only the lower part 

 of the series is exposed. This is divided into two groups by 

 Professor Lapworth. The lower or Bargany Group has a thickness 

 of about 700 feet, the only fossils being the graptolites Monograptut 

 acus and M. priodon. The higher group he called the Straiten 

 Beds, at the base of which are olive-green flags well seen at 

 Drumyork, succeeded by shales containing Monograptus vomerinus, 

 Cardiola fibrosa, Orthonota truncata, and other fossils. The highest 

 beds seen are purplish grits and conglomerates, the exposed thick- 

 ness of the Straiton Group being about 900 feet 



The highest beds referable to the Wenlock Series are well 

 exposed in Lanark, where they are no less than 2200 feet thick 

 (see table below), and yet do not include any beds comparable to 

 those near Straiton ; hence there seems to be a gap in tin- 

 succession, and the full thickness of this series in Scotland is not 

 yet known. 



Ludlow Series. These beds are not found in the main belt 

 nor in the Girvan district, but only in Lanark and the Pentland 

 Hills, where the following succession has been recognised : 



Fwt. 



/"Chocolate-coloured sandstones 

 Downtonian I Conglomerate with quartz pebbles . 



Beds 1 Mudstones and shales with fish and eurypterids 



(.Red and yellow sandstones and mudstoues 

 Ludlow . Red and green shales with Platyceras simulans 

 'Brown sandstones with Orthoceras . 



Wenlock 

 Beds 



Green and grey shales and mudstones 

 Massive sandstones and grits .... j-2200 

 Green, red, and purple shales with eurypterids 

 Starfish, crinoids, and corals .... 



The beds which are bracketed as having a thickness of 2700 feet 

 were formerly grouped with the Old Red Sandstone, but are regarded 

 by the Geological Survey as the equivalents of the Downton and 

 Ledbury Beds. They include a band of shales which has yielded 

 many remains of fish and Merostomata. The fish fauna is of great 

 interest, as two of the genera belong to a family which has hitherto 

 been known only from scales; these genera are Thelodut and 





