IGUANODON AND PELOKOSATJRUS. 197 



strong short feet, protected by broad horny ungueal phalanges, or nails. The fore-legs appear to 

 have been less bulky, and adapted for seizing and pulling down plants and branches : the 

 teeth and jaws demonstrate the nature of its food ; and the fossil remains of coniferous trees, 

 arborescent, ferns, and cycadeous plants, with which its relics are commonly associated, indicate 

 the character of the flora adapted for its sustenance.' 



XVIII. The Pelorosaurus. — The humerus of a terrestrial reptile of enormous magnitude, has 

 lately been discovered by Mr. Peter Fuller of Lewes, in the quarry near Cuckfield, from which 

 many remains of the Iguanodon and Hylseosaurus were obtained in my early researches. This 

 bone more nearly resembles the humerus of the Crocodiles, than that of the Lizards. It Is four 

 and a half feet in length, and of corresponding proportions ; it has a large medullary canal. 

 As to the size of the animal to which it belonged, while disclaiming the idea that any certain 

 conclusion can be drawn from a single bone, I may mention, with the view of conveying some 

 general notion, that in a Gangetic crocodile eighteen feet long, the humerus is one foot: 

 according to this scale the fossil animal would be eighty-one feet in length. I have proposed the 

 name of Pelorosaurus (from -ireXxop — pelbr — monster), or Colossal-saurian, for this new genus of 

 reptiles which Inhabited the country of the Iguanodon.^ 



XIX. SiLiciFicATioN, or petrifaction by flint.— The various forms in which silex occurs have 

 depended on its state of fluidity. In quartz crystals the solution was complete ; in agate 

 and chalcedony it was in a gelatinous state, assuming a spheroidal or orbicular disposition 

 according to the motion given to its particles. Its condition appears also to have been modified 

 by the influence of organic matter. In some polished slices of siliceous nodules, the transition 

 from flint to agate, chalcedony, and crystallized quartz, is beautifully shown. The curious 

 fact that the shells of Echinites In chalk are almost invariably filled with flint, while their 

 crustaceous shells are changed into calc-spar, is probably in many instances to be attributed 

 to the animal matter having undergone sillclfication ; for the most organized parts are those 

 which appear to have been most susceptible of this transmutation. In some specimens the 

 oyster is changed into flint, while the shell Is converted into crystallized carbonate of lime. In 

 a trigonia from Tisbury, formerly In the cabinet of the late Miss Benett, of Norton House, near 

 Wai-mlnster, the body of the mollusk was completely metamorphosed into pure chalcedony, the 

 branchiae or gills being as clearly deflned as when the animal was recent. In specimens of wood 

 from Australia (presented to the British Museum by Sir Thomas Mitchell), which are completely 

 permeated by silex, there are on the external surface some spots of chalcedony, that have 

 apparently originated from the exudation of the liquid silex from the interior in viscid globules 

 filled with air, which burst, and then collapsed, and became solidified in their present form. 



In sillclfied wood, the permeation of the vegetable tissues by the mineral matter appears 

 to have been efl'ected by solutions of silex of a high temperature. In some examples mineraliza- 

 tion has been efl'ected simply by replacement: the original substance has been removed, atom 

 by atom, and the silex substituted in its place. One of the most eminent naturalists and mine- 

 ralogists of the United States, Mr. J. D. Dana,^ suggests that the reason why silica Is so common 



' PhilosopHcal Transactions, for 1S4S, pp. 196—198. 



^ A memoir on this fossil was read before tlie Royal Society, Feb. 14tb, 1850 ; an abstract hiis been published in the Pro- 

 ceedings of the Society. It is entitled, " On the Pelokosacru.s ; an undescribed gigantic terrestrial reptile, whose remains 

 are associated with those of the Iguanodon and other saurians in the strata of Tilgate Forest." It will appear in the Phil. 

 Trans. Part 11. 1850. 



3 American Journal of Science, for January, 1S45. 



