HABITS AND MODE OF OCCURRENCE. 5 



The No. 2 Rhondda Seam and the Graigola or Six-foot Vein of Swansea both 

 occur in the Pennant Grits, the former Hear the base of the series and the latter 

 at 200 yards below the Swansea Four-foot Seam, which forms the base of the Middle 

 Coal Measures in South Wales. 



In Monmouthshire, insect-remains occur in shales over the Mynddislwyn 

 Vein, a seam at the base of the Upper Coal Measures. 



The Durham and South Lancashire Coalfields have yielded insect-remains in 

 measures near the top of the Middle Series, while those recorded from the Derby- 

 shire Coalfield are on a still lower horizon in the Middle Series. Few fossil insects 

 are known from the Upper Coal Measures. 



HABITS AND MODE OF OCCURRENCE OF FOSSIL INSECTS. 



The bodies, and more particularly the wings, of insects, have been entombed 

 in various deposits under conditions difficult to determine. Whatever the condi- 

 tions, they must have been closely related to the habits of life. The older writers 

 claimed that wind-dispersal and water-carriage were the chief agents. Buck! and, 

 for example (' Anniv. Address to the Geol. Soc.,' 1842), supposed " that multitudes 

 of insects have been occasionally drifted by tempests to the sea." Mantell 

 ('Wonders of Geology,' 7th ed., 1857) pointed out that Westwood had drawn 

 attention to the fact that " the streams brought down innumerable insects at 

 certain periods, perhaps those of heavy rain." 



Alfred Russel Wallace (' The Geographical Distribution of Animals,' 1876) and 

 Heilprin ('The Distribution of Animals,' 1887) alike drew attention to the wide- 

 spread occurrence of living insects far out at sea, in some instances still flying 

 strongly. Members of the British Association on their voyage to Australia in 1914 

 verified these statements by the capture of locusts as their vessel proceeded down 

 the Red Sea and into the Indian Ocean. More than a score of locusts were 

 captured on the vessel by which the writer travelled, and many more must have 

 been driven down into the water by the fringe of a simoon into which the vessel 

 entered beyond Aden. 



Many insects are destroyed yearly by falling into streams and rivers after the 

 deposition of their eggs in the water, and by becoming entangled in the 

 surface film. 



The occurrence of whole, or almost whole, insects is more likely to furnish 

 surer proof of the conditions under which life was passed than is the occurrence of 

 wings only, because the bodies, being more compact and much heavier than the 

 wings, are' less likely to have drifted to great distances. Sometimes, as we shall 

 see later when we consider special cases, such as the Coal Measures of Commentry, 

 France, or the remarkable faunal associations of certain of the British fossil insects, 



