FOSSIL CORALLINES. 51 



These Moffat Graptolite-bearing shales are the 

 oldest fossiliferous strata in Scotland, and they attain 

 a total thickness of six hundred feet. They have 

 been grouped by Professor Lapworth into three divi- 

 sions, called Birkhill shales, Hartfell shales, and 

 Glenkiln shales ; and each division is split up into 

 " zones," marked by the presence of certain charac- 

 teristic species of Graptolites. These divisions of the 

 Graptolite shales have been recognized by geologists 

 elsewhere, as in North and South Wales, etc. 



The shales in which Graptolites occur are nearly 

 always of a black colour, and these beds are usually 

 distributed in long lenticular areas through otherwise 

 unfossiliferous rocks. 



Burns' own county of Ayrshire is not without 

 various geological attractions, although the scenic 

 features are not on so grand a scale as elsewhere. 

 In the metamorphosed Lower Silurian slates of Cairn 

 Ryan we meet with abundance of Diplograptus pristis. 

 The Girvan district has long been famous for its 

 Silurian fossils, and recently Messrs. Etheridge and 

 Nicholson have published a splendid monograph upon 

 them. Nearer home, Graptolites are very abundant 

 in the black shales which crop out in the basement of 

 the little gorge on the top of the hill just above Low- 

 wood, on the eastern shores of Windermere, and not 

 more than a couple of miles from Ambleside. They 

 are found on almost every piece of shale, Diplograptus, 

 Rastrites, Graptolithus^ etc., all of them beautifully 



