22G [August, 



Although much of East Hull is industrial, with important oil, paint, 

 and cement works, flour and saw mills, etc., as a whole the city is 

 commercial. Hence, there is little production of deleterious gases, 

 and, for its size, comparatively little dust and smoke. As a rebult 

 there is an abundant growth of vegetation right up to the city 

 boundaries. 



(b.) Middlesbrough also stands on the boulder clay, wdth brackish 

 marshes by the river side, but a very short distance inland are the 

 Jurassic rocks of the Yorkshire Moors, wdiicli are largely covered with 

 heaths, heather, and grass, and in many places with bogs, mainly of a 

 peaty character. The whole riverside is lined w^ith iron and chemical 

 works, which throw out enormous quantities of smoke, dust and 

 noxious gases, the result being that, in the immediate neighbourhood 

 of the works, vegetation has a hard fight to survive at all, and even at 

 some distance, the struggle is frequently a severe one. 



(c.) In the Tyne district the lower lands are again covei-ed with 

 boulder clay, but the surface is a very varied one, and there are many 

 uplands of sandstone and magnesian limestone, with mountain lime- 

 stone as we near the Penniues. The chief occupations are coal-mining, 

 shipbuilding, and engineering industries, while chemical works of 

 various kinds are not iew, and at one time were much more important. 



After this preliminary survey, it is possible to gain a better com- 

 parative grasp of the influences at work tending to the survival or 

 extinction of insect life in the areas under consideration. It should be 

 understood, however, that certain factors have intentionally been 

 omitted, such as inclement weather of various kinds — drought, rain, 

 late frosts, etc. — previous exhaustion of the food supply by other 

 insects, migration, etc., my idea being rather to give examples of 

 influences which are of a more local character and which do not there- 

 fore apply to the country as a whole. 



III. — The Htjmber Area. 



In the Hull district the insect fauna is comparatively poor in 

 numbers, both of species and individuals ; this is doubtless largely to 

 be attributed to the clayey soil, but there is no doubt that in former 

 times it was much richer. Here one potent cause of the reduction of 

 insect life is undoubtedly the drainage, which has reclaimed the greater 

 part of the marsh-land ; hence the Swallow-tail Butterfly (Papilio 

 machaon L.) is now extinct, though it was once found near Beverley ,(^) 



(1). Haworth, L pidoptfrn Brltunnka, lSO-1, p. 'll. 



