1854.] WESTWOOD —FOSSIL INSECTS. 391 



The Museum of Practical Geology in Jermyn-street also possesses 

 a fine series of fossil insects from the Purbecks. This series agrees 

 in general characters with the Rev. Mr. Brodie's collection, but com- 

 prises several specimens of Dipterous insects in a much more perfect 

 condition. 



In the British Museum also there are a few fossil insects from the 

 same formation ; and there are several other specimens in the Cam- 

 bridge and Dorchester Museums. 



Summary. 



The microscopical examination which I have been compelled to 

 make of so many hundreds of fossil insect-remains, for the most part 

 in a fragmentary condition, from the Lower Purbecks of Dorset, 

 although beyond measure tedious from the unsatisfactory results 

 afforded by the nature of the specimens, has still enabled me to arrive 

 at some results, and to form a general comparison of these insect- 

 deposits with those which I similarly investigated whilst preparing 

 the plates of Mr. P. B. Brodie's work on the fossil insects of the 

 Wiltshire Purbecks, &c. 



If we take into consideration the small, and even minute size of 

 the great majority of the insects, and indeed of the whole of the 

 Coleoptera, which have been passed under review, the idea, that we 

 have before us the wreck of an Insect Fauna of a temperate region, 

 is at once raised ; for although it would be rash to assert that a mass 

 of remains of the existing tropical insects might not be accumulated 

 in which a large quantity of minute beetles and flies would not be pre- 

 sent, yet I cannot conceive any process, either arising from currents 

 of water, or chemical dissolution of insect matter, which would carry 

 ofF or destroy the many gigantic forms of insect life always occurring 

 in the tropics. 



The fossils before us show abundant evidence of the presence of 

 numbers of Lignivorous species, such as the ElateridcB and Bupres- 

 tidce ; but we nowhere find amongst them traces of the great Lamel- 

 licorn and Longicorn beetles. Herbivorous insects also occur in consi- 

 derable numbers ; but we do not meet with the gigantic Grasshoppers 

 and Locusts of tropical climates. It has indeed been suggested that 

 the remains may be those of insects living in a temperate climate and 

 carried by currents to a tropical region ; and Prof. E. Forbes has 

 instanced the fact that he found shells of a temperate type, natives 

 of the upper parts of the great range of the Atlas Mountains in 

 Africa, brought down by currents and resting in the lower regions 

 among shells of a tropical character. But, in order that the analogy 

 should hold good, it seems to me necessary that we should find 

 amongst the remains, not a single specimen or two (as in the case 

 of the wings of the large Ants above-mentioned), but the remains of 

 a great majority of tropical species mixed \\\y with a smaller number 

 of temperate forms. I must leave geologists to discover or to suggest 

 the action which could have brought together and deposited such 

 great masses of insect-remains as we find in many of the slabs of 

 stone in these collections, and of which PI. XVI. fig. .3 will afford 

 an idea. Entomologists, however, are perfectly well aware that sudden 



VOL. X. — PART I. 2 E 



