66 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 5, 



The slab in question is seven feet long by three and a half feet 

 broad. It contains none of the footprints of the so-called Chirothe- 

 rium {^Labyrinthodon, Owen), but is full of those of smaller reptiles, 

 apparently both Emydian and Batrachian, besides others which may 

 have been made by birds. It is remarkable for the singular compli- 

 cation of cracks it presents, these forming a net-work more elaborate 

 than I have noticed in other specimens*. It will readily be seen from 

 an examination of the slab that the cracks took place after the foot- 

 marks had been impressed on the marly silt, which must first of all 

 have been slowly and quietly deposited on the firm sand beneath. 



It would also appear from this slab, that after the deposition of 

 this thin coherent bed, which would not originally have exceeded 

 an inch in thickness, the waters must have retired for a time without 

 reflux, and that during this time many kinds of animals, terrestrial 

 as well as amphibious, walked over the surface, while a continued 

 process of drying was contracting the whole surface and thus form- 

 ing a net-work of cracks over it. After this process had gone on 

 until the drying was complete, another deposit of arenaceous sedi- 

 ment took place, filling up the cracks and depressions of the surface 

 and forming one homogeneous mass of sandstone. 



On carefully examining the reversed impressions seen in relief on 

 the slab, we may recognise at least four separate and well-defined 

 kinds, besides several others which either from their minuteness or 

 indistinctness are not easily characterized. There are also two 

 sweeping mouldings of slight elevation that traverse the face of the 

 specimens in oblique directions. Owing to the cracks that have 

 taken place, the marks are often divided and sometimes are shifted 

 laterally. This is also the case with the lateral moulding. 



Of the larger footprints, there are about twenty running princi- 

 pally in one direction. They are disposed in parallel rows, with a 

 distance of nine inches from the tip of one toe to that of the other 

 in each row, while each print in the one row is placed opposite the 

 middle point between the two others in the corresponding row. The 

 impressions, or rather the moulds, rise above the plane of the slab for 

 about three-eighths of an inch. The length of each footmark is two 

 inches, and the breadth an inch and a half. The highest point in 

 the mould (the deepest impression therefore) seems to correspond 

 with the heel, which in several cases appears to have penetrated 

 through the soft clayey mass to the hard sand. On each side of se- 

 veral of the footprints there are impressions of short toes or claws, 

 while round the front of each there is a semicircular and shallow 

 groove or waved hollow, such as might be occasioned by the soft 

 mud being pressed forwards and raised by the weight of the foot. 



The larger impressions (PI. V. fig. A.) seem to be intimately con- 

 nected with the two moulded tracks that sweep over the face of the 

 slab, for these tracks run parallel and midway between the two rows 

 of footmarks, and were evidently formed before the clay had dried. 



* The slab from Ilessberg, figured in Dr. Buckland's Bridgewater Treatise, 

 offers the nearest resemblance in this respect, but is not so completely covered 

 with the reticulations. 



