DISTRIBUTE INSECT VARIETY. 271 



The older insects of the several epochs, as far as can be worked 

 out, harmonise in character with the vegetation, while those 

 inhabiting Europe in Tertiary time are more or less established 

 as Indian, Ethiopian, or American in type. Agreeably too with 

 this, a trace of the last glacial flora and insect fauna is found 

 isolated on the tops of European mountains. The present insect 

 fauna of the European and North Asiatic region i-esembles 

 the North American, with that of California and Chili, 

 united by the cold elevated ridge of the Rocky Mountains 

 and Andes — a fact harmonising with the common Europeo- 

 American vegetation at the close of the Tertiary. Although the 

 Australian and South African insects which characterise the 

 early portion of the third period are not generally recognised as 

 existing on the present Palaearctic area, still we find some 

 unmigratory species, as the Silver-lines Moth, now localised on 

 the diverse vegetation of Europe and Australia, and these there- 

 fore should be the more ancient. 



If we next cast a retrospect on the laws governing the 

 migration of plant and insect with the present operation of 

 nature, in modifying and adapting species thus submitted to 

 changed circumstances, and proceed to summon the comitless 

 array of ages these laws have had force with the Articulata, 

 since the first vermes became by immutable mandate a chitineous 

 myriapod, or the fin-like extensions of its tracheae took alar 

 forms — if we, then, consider the effect of these laws at intervals 

 of vast ages, attested in the varied aspect of fossil insects from 

 Palaearctic areas, and weigh their relations in character and mag- 

 nitude to species existing on these and other areas, here, as in 

 allied departments of Palaeontology, we are led to postulate 

 cooling, or more probably, as Mr. Page has propounded, a 

 recurrent heating and refrigeration of the northern hemisphere, 

 most naturally accompanied by general land elevation and depres- 

 sion compelling the migration of terrestrial species. The colder 

 circles of this life are, according to Mr. Page, evinced by the 

 Azoic Grits of Cambria, the Old Red conglomerates, Permian 

 breccias, and the boulder clays of the Pleistocene epoch — the 

 intermediate warmer mark those of the Carboniferous^ Oolite, and 

 earlier Tertiaries, whose floras once stretched and have left their 

 remains beneath the frozen Arctic. In short, there is seen a 



