RAMBLES OF A GEOLOGIST. 441 



shows not only the enamelled plates of the frontal buckler, 

 but also the strange mechanism of the palatal teeth, with the 

 intervening cavities that had lodged both the brain and the 

 occipital part of the spine. The fossils on the top of the 

 cliffs here are chiefly Dipterians of the two closely allied ge- 

 nera, Diplopterus and Osteolepis. 



A little farther on, I found, on a hill-side in which ex- 

 tensive slate-quarries had once been wrought, the remains of 

 Pterichthys existing as mere patches, from which the colour 

 had been discharged, but in which the almost human-like 

 outline of both body and arms were still distinctly traceable ; 

 and farther on still, where the steep wall of cliffs sinks into 

 a line of grassy banks, I saw in yet another quariy, ichthyo- 

 lites of all the three great ganoid families so characteristic of 

 the Old Red, Cephalaspians, Dipterians, and Acanthodians, 

 ranged in the three-storied order to which I have already 

 referred as so inexplicable. The specimens, however, though 

 numerous, are not fine. They are resolved into a brittle bi- 

 tuminous coal, resembling hard pitch or black wax, which is 

 always considerably less tenacious than the matrix in which 

 they are inclosed ; and so, when laid open by the hammer, 

 they usually split through the middle of the plates and scales, 

 instead of parting from the stone at their surfaces ; and re- 

 semble, in consequence, those dark, shadow-like profiles taken 

 in Indian ink by the limner, which exhibit a correct outline, 

 but no details. We find, however, in some of the genera, 

 portions of the animal preserved that are rarely seen in a 

 state of keeping equally perfect in the ichthyolites of Cro- 

 rnarty, Moray, or Banff, those germinal bones of the Coc- 

 costeus, for instance, that were prolonged beyond the plates 

 by which the head and upper parts of the body were covered. 

 Wherever the ichthyolites are inclosed in nodules, as in the 

 more southerly counties over which the deposit extends, the 

 nodule terminates, in almost every case, with the massier 



