THROUGH THE LOWER AND UPPER STRATA. 



23 



The remains of winged insects have sometimes been found in the 

 upper secondary strata in England, particularly in the calcareous 

 slate of Stonesfield, Oxfordshire, where numerous impressions of 

 the elytra, or hard cases which cover the wings, of coleopterous in- 

 sects occur. Professor Buckland very ingeniously conjectures that 

 these winged insects might serve as food for the flying lizards (Pte- 

 rodactyli) that are found in the same strata, and were cotemporane- 

 ous with them. Of all the four grand divisions of the animal king- 

 dom, the Articulated has supplied the smallest number of fossil or- 

 ganic remains. 



Molluscous Animals. — Shells of these animals, chiefly bivalves, oc- 

 cur in the limestones of the transition series ; but the number of the 

 species is comparatively small. Some chambered shells, particularly 

 orthoceratites, are found in transition limestone. 



In the secondary strata that cover the transition series, shells of 

 molluscous animals, both bivalves and univalves, are more abundant, 

 and the number of the species is greatly increased. 



It is in the lower strata of this series that chambered shells, such 

 as nautilites and ammonites, first become numerous : some species 

 are continued into the chalk strata, but no ammonites are found in 

 the strata above chalk. Trochiform or top-shaped spiral univalve 

 shells first appear in the lower part of the secondary series, but be- 

 come more numerous in the upper part of this series. • In the tertia- 

 ry strata above chalk, the species of univalve shells greatly exceed 

 those of the bivalves : in the lower strata, the reverse is the case. 

 We may further remark, that, as the tertiary strata are the most re- 

 cent of regular rock formations, so the organic remains which they 

 contain, bear a closer resemblance to the shells of molluscous ani- 

 mals living in our present seas, than what are found in the more an- 

 cient strata. Some of the shells in the upper part of the tertiary 

 strata appear, indeed, to be identical with those of existing species. 



The different classes and orders of molluscous animals that have 

 left their remains in the lower and the upper strata, doubtless pos- 

 sessed, each, the peculiar organization that best enabled them to ex- 

 ist and multiply under the peculiar condition of our planet, that wa& 

 cotemporaneous with the epoch of their creation. When this con- 

 dition was changed, their numbers were diminished, or they disap- 

 peared entirely, and were succeeded by different races, with an or- 

 ganization adapted to other modes of existence, and to the new cir- 

 cumstances in which they were placed. Such are the legitimate in- 

 ductions which we appear justified in making, from the organic re- 

 mains in the different strata. The further consideration of this inter- 

 esting enquiry will be resumed in the succeeding chapters. 



Vertehrated Animals are arranged under four classes : — fishes, 

 reptiles, birds, and mammiferous animals. Remains of fishes are 

 exceedingly rare in transition rocks ; but they appear, decidedly, in 

 the lower secondary strata. The entire bodies are, sometimes, well 



