GEOLOGY OF DERBYSHIRE. 237 



is common, and may be known by its shape something resembling' 

 an Ammonite, except that the whorls are elevated towards one side. 

 The Bellerophon is a wide round shell, whose inner whorls are 

 almost wholly concealed by the external ones ; it is supposed to be 

 allied to our Argonauta. Of chambered shells, the mountain lime- 

 stone contains one or two species of Nautilus ; a kind of Ammonite, 

 called the Goniatite, a small nearly spherical shell generally, with 

 the septa of the chambers bent into acute angles ; and the Ortho- 

 cera, the best idea of which may be gained by imagining a Nautilus 

 unrolled and made straight. Some fishes' teeth have been found in 

 the limestone at Ashford. 



It is worthy of notice, that when any fossils are found in the 

 chert, the cast only of them is preserved, as is seen in the casts of 

 the internal part of the Encrinite, so abundantly found in the chert 

 and commonly called screw stones. The way in which the shells 

 and other remains are found embedded in the solid rock is often 

 remarkable, and when examined attentively will be found to afford 

 many evidences of their having lived and died in the spots where 

 they are now found, and of the slow and gradual process by 

 which they have been entombed. Some species of Producta were 

 provided with spines, and these may occasionally be found still 

 perfect in all their delicate beauty adhering to the shell. Many, 

 if not the majority, of the shells are filled only by crystals of 

 carbonate of lime, and not by the compact matter of the rock, 

 which shows that they were embedded whole and unfractured, 

 that not even the ligature of the hinge had given way, and that 

 the interior matter had only gained access to them by percolation 

 through the substance of the shell.* Others, again, occur in single 

 valves, and some have evidently been broken before they were em- 

 bedded in the rock, as we might now find shells loose or broken on 

 the floor of our seas. Occasionally, about the junction of the lime- 

 stone and the shale, I have seen beds in which great quantity of 

 fragments of shells and other things occurred, as if currents which 

 had the power of drifting shells began then to prevail. Everything, 

 the more we examine the rocks in their native home, instead of 

 studying them by the help of cabinets of specimens, tends to fix in 

 our minds the belief that we are looking on things which have been 



• In a quarry near llopton, where the shells are very perfect, I have fre- 

 quently, on breaking one open, found a black shining substance, splitting 

 iiiin small i iiIk-s, apparently pure bitumen. Could it be derived from the 

 aniinal matter of the creature which inhabited the shell P No black marks 

 were visible externally, nor was any black stone in the neighbourhood. 



