198 RAMBLES AND REVERIES. 



liness which only appears to those who perceive the 

 hidden meaning that lies beneath the surface of 

 Nature's works. 



Silurian trilobites occur in large numbers also 

 near Hereford, where Pkacops, Homalonotus, and 

 other genera may be found. 



The Devonian strata furnish trilobites, but not in 

 anything like the profusion that characterises the 

 Cambrian and Silurian beds. Dr. Taylor refers to 

 Newton Abbot as being a good hunting-ground for 

 them, but I was not fortunate enough to obtain any 

 when I visited that romantic district. 



The carboniferous limestone of the Derbyshire 

 Peak is pretty sure to reward the searcher after 

 trilobites. At Castleton I met with Phillipsia, 

 which along with Griffithsides is frequently to be 

 obtained from the shales and belts of limestone in 

 that locality. These are of great interest as pre- 

 senting the last scions of a noble race which in 

 earlier geological times enjoyed a sort of supremacy 

 over the less richly endowed, though in some respects 

 more highly developed, Molluscan fauna. 



In geological range, as just intimated, the tri- 

 obites are confined to the Primary rocks. They 

 were exceedingly prolific in the Cambrian seas, 

 having reached almost their zenith of size and 

 development in early Cambrian times ; rapid varia- 

 tion proceeded during the Silurian age, while distinct 

 degradation marked the Devonian history of these 

 creatures ; and in the next period, the Carboniferous, 

 they became rare and small, ultimately passing out 

 of existence altogether before the advent of that 



