12 



"Coprolitic origin, but that it had since been satisfactorily 

 " shewn that tliey were detrital materials from the bed just 

 "mentioned. The Crag nodules (he states) only differ from 

 " those of the London clay in having been slightly rolled and 

 " somewhat modified by having had a portion of iron pyrites 

 *' converted to oxide of iron." Professor Henslow then goes on to 

 say, that the " Cetotolites described by Professor Owen, numerous 

 " fragments of bones, and many highly mineralized fossils found 

 " in the Crag, must he classed as detrital materials from the 

 ''London clay. The genuine Crag fossils are readily separable 

 " from those of the Eocene period by their not being mineralized, 

 " and such is the case with fish bones, crustacean and other 

 "remains, as well as the testacean shells so abundant and well- 

 " known in the Crag."* 



As I have no knowledge from any observations of my own 

 respecting the true origin of these nodules, I have thought it 

 better to state Avhat I have just mentioned, in Professor 

 Henslow's own Avords. The formation of the nodules themselves, 

 to whatever bed they rightly belong, is due to the aggregation 

 of earthy particles round the organic remains with which they 

 are mixed up, at the time the bed was deposited, these animal 

 remains serving as a nucleus (like the sponges, &c., in flints) and 

 favouring the aggregation by the chemical changes attending 

 decomposition. The Cetotolites alluded to in Professor Henslow's 

 paper just quoted, have a degree of interest in connection with 

 this subject, from the circumstance of their having been discovered 

 by him at the time that he was examining the Eed Crag in 

 search of these nodules. They are the petro-tympanic bones 

 of whales* ears in a fossil state, as the name signifies, and 

 specimens having been sent up by him to Professor Owen, the 

 latter gentleman pronounced them to have belonged to no less 



* Rep. Brit. Asso., 1847, Sect., p. 64. 



