63 
About its origin, I have consulted one of the best practical 
Geologists of this county, a gentleman well known to you, and am 
informed by him that there is no doubt that this tract of country 
was actually a range of coast sands, at a comparatively recent point 
of the Post Glacial period, while the great valley of the fens was 
still submerged. This range of sands, however, does not appear to 
extend anywhere near to the present coast. The nearest sea is the 
Wash, upwards of twenty miles away, and the Eastern coast with 
its belt of sandhills is forty miles distant, the intermediate country 
being, in both cases, of a totally different character. 
Although the Post Glacial epoch is, I believe. Geologically 
speaking, a very recent one, the actual length of time since passed 
is so great, that I presume few Geologists would venture to compute 
it, even in thousands ot years, dhe occurrence, therefore, at the 
present time of these coast insects, on this ancient sea-shore, is a 
ciicumstance of considerable interest, particularly as they appear to 
be bj no means scarce there — indeed Gclechia deserMla swarms 
in hundreds in the rough fields and among the stunted furze bushes 
and the question naturally arises, by what means they became 
settled in so congenial a spot. The immediate answer to be 
expected is “ By migration,” and abundant theories instantly crop 
up of chance specimens carried across country the whole distance 
by storms of wind. I am, however, from knowledge of their 
habits utterly unable to accept this solution, especially in the case 
of the weakly constructed Anerastia lotella and the little Gelechife. 
I hold it to be physically impossible for their delicate frames to 
survive such treatment. 
The “blown across” theory may possibly hold good sometimes 
in the case of strong winged, day flying insects, such as the butter- 
flies, which, provided the sun be shining, are ready to brave a 
considerable amount of wind, but with insects whose special aim 
is to avoid it, and whose instinct in foreseeing changes of weather 
is so fine as never to seem at fault, such a solution is utterly unten- 
able. Moreover, the “blown across” theory is only applicable to 
the comparatively level surface of the sea where the wind has free 
course. In crossing a country covered with scattered trees and 
with occasional hills and other inequalities of surface, the disturb- 
ing currents caused by them would soon and certainly precipitate 
such matters to the ground, or enable them to reach it. 
