ANNUAL ADDRESS, MDCCCLXXIII. 31 



geological chronology we become acquainted with the 

 existence of fishes. From the specimens on the table it 

 will be seen that Silurian limestones are of a dark grey 

 colour, more or less argillaceous or clayey, and interstratified 

 with grey shales. The rock is often subcrsytalline, and 

 contains in veins fine well-formed crystals of carbonate of 

 lime. 



In ascending in the order of time from the Silurian 

 epoch, we come to that of the Devonian, or Old Red 

 Sandstone. The study of this system immortalised the 

 name of the lamented Hugh Miller. This period is doubly 

 interesting as bringing to light the existence of the earliest 

 known insects. Four species of the order neuroptera have 

 been found. One species of the genus ephemera, of which 

 the ephemera vulgator or green and grey drake flies of 

 our rivers in June are examples, so useful in trout fishing, 

 and so much prized by anglers, among whom is my esteemed 

 friend Mr. Ward, who does not wholly confine his pisca- 

 torial studies to palasontological times I say one species 

 found in Devonian rocks measured five inches in expanse 

 of wing. I do not know how this fact agrees with the 

 development theory of Mr. Darwin, but I think the ap- 

 pearance in Dovedale of a green or grey drake fly measur- 

 ing five inches across the wings, some fine afternoon in 

 June, would astonish not a little both trout and Piscator. 

 Dr. Dawson remarks that in one type there is the stridu- 

 lating or musical apparatus like that of the cricket, and 

 that in this structure we are introduced to "the sounds of 

 the Devonian woods bringing before our imagination the trill 

 and hum of insect life that enlivened the solitude of these 

 strange old forests." (Lyell's Student's Elements, p. 440.) 

 The limestones of the Devonian period are considerably de- 

 veloped in Devonshire, at Plymouth, Devonport, and Ilfra- 



