82 Mr. Toulmin Smith on the Ventriculidse 



and one that may fairly entitle him who enters upon it to expect 

 to meet with indulgence/' — an indulgence, however, which those 

 best qualified to judge of the value of such observations will, 

 happily, be also most able and willing to yield*. 



My first step was to obtain as large and varied a series as 

 possible. I have in truth examined and compared with laborious 

 care several thousand specimens, of which certainly upwards of 

 one thousand are at this time in my own collection. These spe- 

 cimens are in all conditions and from various localities. 



But I soon felt a new difficulty. These bodies exist both in 

 the chalk and in the flint, substances about as different as well 

 may be. I saw that much error and inconsistency had arisen 

 from not comparing and regarding the differing conditions in 

 which these fossils exist in such different substances. Hence 

 a preliminary step seemed to be, an examination of the nature 

 and mode of formation of the flints themselves. The conclusions 

 resulting from that examination have, to a great extent, been com- 

 municated in two papers in the ' Ann. and Mag. of Nat. Hist/ for 

 January and May of the present year. 



The exposition given by Dr. Turner f of the origin of the sili- 

 ceous fluid, — in the solution of silex consequent on the disinte- 

 gration of the felspar of igneous rocks, at which moment of dis- 

 integration the silex is liable to free solution in water, — was con- 

 sistent and satisfactory. But no consistent or satisfactory view 

 could be discovered explanatory of the modes and forms in which 

 the flint is actually found. I endeavoured in the above-cited 

 papers to show that those modes and forms are owing to the very 

 rapid solidification of the siliceous fluid — induced by special cir- 

 cumstances — combined with the activity of molecular attraction : 

 that those special circumstances were generally the presence of 

 an organic body which acted as a nucleus, — the softer bodies 

 being more operative in this respect than the harder : that some- 



* One of the most pleasing duties of the student of natural history is to 

 acknowledge and reciprocate the assistance received from, and always so 

 ready to be rendered by, other naturalists. I take this opportunity of 

 acknowledging my obligations to Professor Owen for, among other things, 

 affording me the opportunity of fully examining several recent specimens 

 of the highest interest, some of which I shall have occasion particularly to 

 mention hereafter; to Mr. Morris, the well-known author of the ' Catalogue 

 of British Fossils,' for assistance rendered in more ways than it would be 

 easy for me to enumerate; to Mr. Tennant of the Strand, and Mr. Harris 

 of Charing in Kent, who have each placed at my disposal several valuable 

 specimens with the liberal permission to make any sections I desired ; and 

 to Miss Emma Naylor of Wakefield for the donation of many fine specimens 

 of recent British Polypifers collected by herself. To many others my 

 acknowledgements are also due, for the loan of specimens, both fossil and 

 recent, for examination and comparison. 



t Lond. and Ed. Phil. Mag. vol. iii. p. 25. 



