286 THE CAUSES WHICH 



can be induced in insect colour ; but the more interesting topic 

 is a possible application of analysis to account for the selection of 

 the geological foi'mations. " The Large Heath Butterfly is a 

 very light insect (var. Tijphon) in Cumberland and Scotland on 

 high hills; whilst on low moss land, on which the water is charged 

 with iodine, in Cumberland, Westmoreland, and Lancashire, it is a 

 rich fulvous brown insect, larger and stronger built ; and when 

 these are acted upon by hydrochloric acid gas they assume the 

 exact colour of the hill specimens. The Dark Annulet Moth 

 [GnopJios ohscurarid) on chalk lands is a light-coloured grey or 

 drab insect. In Carboniferous limestone districts it is a lead- 

 coloured insect, whilst on the New Red sandstone, ' Keuper' 

 formation, it varies from a rich ochreous colour where oxide of 

 iron is present in the soil, to a dark, almost black, insect on the 

 white sandstone parts of the New Red formation,, thus clearly 

 pointing to geologically-caused changes of colour. Any of these 

 latter forms, acted upon by chlorine, appear as light-coloured 

 grays. The same remarks apply to Dranihacia car2)02)Iiaga. On 

 chalk it is light buff ; on ' New Red ' here, darker ; bvit all buff 

 on ' Cambrian ' at Llangollen ; and at Penmaenbach darker still, 

 buff or ochreous brown ; and on quartzoise early rock rich dark 

 cold grey-brown, as in the Isle of Man, and at Howth, in Ireland, 

 ochrey shades being rarely observable upon them ; but, acted 

 upon by hydrochloric acid gas, they all turn to beautiful bright 

 light fawn buffs^ veritable Carpophaga of the chalk.^^ The 

 writer, however, suggests that some varieties we might be inclined 

 to attribute to certain formations may be the result of a food 

 proper to the soil. Thus in the case of the Welsh Wave Moth 

 {Acidalia contignarui), bred continuously on heather from the 

 moss lands, all specimens become varieties, fumose specimens, 

 whilst when fed upon low succulent plants they were large 

 light-coloured specimens, rarely darkish, but never so dark as 

 when fed upon heath from the moss.^ 



Some general rules of variation in European butterflies and 



* The varieties are figured in Newman's Entomologist, Vol. XII., p. 65-67. 

 In this paper, b)' Messrs. Fryer and Capper, it is stated that the dark variety on 

 Bettws-y-Cocd is larger, and occurs at a greater elevation than the light hone- 

 coloured one at Llanfairfechen, and that it likewise is found, as I conclude, on 

 the Cevennes Mountains. Guenee, "Hist. Nat.," Vol. IX., p. 464. 



