222 LYELL'S ELEMENTS OF GEOLOGY. 



Oolite Group Stonesfield Slate. 



broad band of country from Bradford, in Wilts, to Tetbury, in 

 Gloucestershire. These calcareous slabs, or tile-stones, are sepa- 

 rated from each other by thin seams of clay, which have been 

 deposited upon them, and have taken their form, preserving the 

 undulating ridges and furrows of the sand in such complete 

 integrity, that the impressions of small footsteps, apparently of 

 crabs, which walked over the soft wet sands, are still visible. In 

 the same stone the claws of crabs, fragments of echini, broken 

 shells, pieces of drift wood, and other signs of a neighbouring 

 beach, are observed. 



The slate of Stonesfield has lately been shown by Mr. Lons- 

 dale to lie at the base of the Inferior Oolite. It is an oolitic 

 shelly limestone, only six feet thick, but very rich in organic 

 remains. It contains some pebbles of a rock very similar to 

 itself, and with them the fossil remains of belemnites, trigonise, 

 and other marine shells. Besides fragments of wood. 

 Fig. 218. which occur in all parts of the oolitic group, there are 

 many impressions of ferns, cycadeoe, and other ter- 

 restrial plants. Several insects also, and among the 

 rest, the wing-covers of beetles, are perfectly pre- 

 served, (see Fig. 218.) some of them approaching 

 nearly to the genus Buprestis.* The remains, also, 

 of many genera of reptiles, such as Plesiosaurus, 

 Crocodile, and Pterodactyl, have been discovered in 

 the same limestone ; and, what is still more remark- 

 able, the jaws of at least two species of mammiferous 

 quadrupeds, allied to the Didelphys, or opossum. 

 These fossils afford the only example yet known of 

 terrestrial mammalia in rocks of a date anterior to the Eocene 

 period. 



This exception is the more deserving of notice, because even 

 no cetacea have as yet been observed in any secondary strata, 

 although certain bones, from the great oolite of Enstone, near 

 Woodstock, in Oxfordshire, have been cited, on the authority of 

 Cuvier, as referable to this class. Dr. Buckland, who has stated 

 this in his late Bridgewater Treatise,! has had the kindness to 

 send me the supposed ulna of a whale, in order that Mr. Owen 

 might examine into its claims to be considered as cetaceous. It 

 is the opinion of that eminent comparative anatomist, that it can- 

 not have belonged to the cetacea, because the fore-arm in these 

 marine mammalia is invariably much flatter, and devoid of all 

 muscular depressions and ridges, one of which is so prominent in 

 the middle of this bone. (See Fig. 219.) In saurians, on the 



* See Buckland's Bridgewater Treatise. 



t Vol. i. p. 115; 



