APHIDES OP FLORISSANT. 157 



which they grew; and within present memories they had 

 a size from five to six metres (diameter?). Specimen- 

 hunters have now greatly injured these fine fossil 

 examples.* 



Trachytic rocks, lavas, and remnants of old geysers, 

 are in the immediate neighbourhood. These last are 

 indicated by deep and polished funnel-holes sufficiently 

 large to conceal a man, and their presence shows that 

 formerly volcanic energy was periodically exerted over 

 a considerable district. 



The most prolific insect beds of Florissant appear 

 to be the drab-coloured shales above indicated, of about 

 sixty centimetres thick (=23 - 6 inches), the chemical 

 constitution of which has been investigated by Dr. M. 

 "Wadsworth, of Cambridge, Mass. He is of the opinion 

 that clouds of volcanic ashes must have fallen into a 

 still lake. Perhaps a"moya" or a mud-flow "may 

 have been worked over by water, covering the under- 

 lying beds and entombing the interesting remains now 

 brought to light. The matrix is described as "a grey 

 mass containing fragments of feldspar, augite, &c, 

 cemented by a fine earthy ground-mass." These beds 

 are wonderfully prolific in fossils, and in this respect 

 they even outstrip the famous deposits of (Eningen. 



Mr. S. H. Scudder has already described 250 species, 

 and thinks that probably at least 1000 more may 

 be separated from the rich masses obtained from 

 Florissant. 



Hemiptera form about 11 per cent, out of the whole 

 order Insecta, and they are nearly in the same pro- 

 portion as those which occur at (Eningen. Mr. S. 

 H. Scudder thinks, however, that the fauna of his 

 district more nearly approaches that of Radoboj ; for 

 40 per cent, is represented by Hymenoptera at Floris- 

 sant ; against 14 per cent, only at (Eningen. On the 

 other hand, as at Radoboj, ants are largely preserved; 

 as many as 4000 specimens have been examined, yielding 

 to Mr. Scudder no less than fifty separate species. 



* ' Bull. Geol. Surv.,' vol. vi, p. 284, S. H. Scudder. 



