ANCIENT SLATE-INSCRIPTIONS. 



53 



easy to work, at Low-wood on the eastern side of 

 Lake Windermere, in the slaty shales of the railway 

 cutting near Conway station, in the slate quarries 

 of Llansantfroid in Denbighshire, in the Arenig 

 rocks of Port Madoc in North Wales, and of 

 Ramsey Island, at St. David's, and other places 

 in South Wales, in the Ludlow series of the Upper 

 Silurians, and in the 

 Wenlock shales of 

 Builth. 



The zoological charac- 

 ters of the graptolite are 

 not easy to discover from 

 their fossil remains, 

 especially as there is no 

 known living form with 

 which they can be 

 grouped. The truth is 

 that our modern classi- 

 fications, whilst extensive 

 enough to include within 

 their limits every organic 

 form both extinct and 

 surviving, require a few spaces to be left in 

 which to place some fossilized remains of creatures 

 that are totally unlike anything now existing. 

 Graptolites are of this kind. While presenting 

 a few similarities to the broader characteristics 

 of Hydrozoa, they yet differ so radically from all 

 other Hydrozoa as to lead Professor Nicholson 

 to set them apart in a sub-class which he calls 

 Graptolitoidea, corresponding to Allnian's Rhab- 



FIG. IQ.Sertularia fusca, 

 (a) Colony, natural size, 

 (*) Calycles, magnified. 



