Ch. XX.] ENGLISH EOCENE FORMATIONS. 277 



of the insects have been supposed identical with species now 

 living*. These insects have been almost exclusively procured 

 from a thin bed of grey calcareous mar], which passes into an 

 argillaceous limestone found in the quarries of gypsum near 

 Aix. The rock in which they are imbedded is so thinly lami- 

 nated that there are sometimes more than 70 layers in the 

 thickness of an inch. The insects are for the most part in 

 an extraordinary state of preservation, and an impression of 

 their form is seen both on the upper and under laminse, as in the 

 case of the Monte Bolca fishes. M. Marcel de Serres enume- 

 rates 62 genera belonging chiefly to the orders Diptera, 

 Hemiptera and Coleoptera. On reviewing a collection brought 

 from Aix, Mr. Curtis observes that they are all of European 

 forms and most of them referrible to existing genera f. With 

 the single exception of an Hydrobius, none of the species are 

 aquatic. The antennae, tarsi, and trophi are generally very 

 obscure, or distorted, yet in a few the claws are visible, and the 

 sculpture, and even some degree of local colouring, are pre- 

 served. The nerves of the wings, in almost all the Diptera, 

 are perfectly distinct, and even the pubescence on the head of 

 one of them. Several of the beetles have the wings extended 

 beyond the elytra, as if they had made an effort to escape by 

 flying, or had fallen into the water while on the wingj. 



BASINS OF LONDON AND HAMPSHIRE. 

 The reader will see in the small map above given (No. 62,, 

 p. 275,) the position of the two districts usually called the 

 basins of London and Hampshire, to which the Eocene for- 

 mations of England are confined. These tracts are bounded 

 by rising grounds composed of chalk, except where the sea 

 intervenes. That the chalk passes beneath the tertiary strata, 

 we can not only infer from geological data, but can prove by 

 numerous artificial sections at points where wells have been 

 sunk, or borings made through the overlying beds. The 



* M. Marcel de Serres, Geog. des Ter. Tertiaires du Midi de la France, 

 t Murchison and Lyell. Ed. New Phil. Journ., Oct. 1829. 

 J Curtis, ibid., where figures of some of the insects are given. 



