ANNIVERSARY ADDRESS OF THE PRESIDENT, CXXX111 



now receives organic remains after they have been critically examined 

 and described by the zoologist or botanist, and has only to apply 

 them to the practical objects of his own science. "Whilst, however, it 

 is easy to allot to the palaeontologist and to the geologist their re- 

 spective tasks, it is not so easy to separate the objects of physical 

 geology from those of pure or descriptive geology, upon the same 

 principle that a perfect geographer may be expected to be conver- 

 sant with both natural and physical geography : it is, indeed, the 

 object of the geologist not only to determine the age of a deposit, but 

 also the physical circumstances under which it was formed. The 

 latter and truly philosophical branch of the subject has always been a 

 favourite study of our able fellow-member, Mr. Godwin- Austen ; and 

 in the paper I am about to notice, he founds upon a simple fact a very 

 ingenious speculation. The " fact " is, that in the chalk about two 

 miles south of Croydon was found a boulder of granite, associated 

 with other detritic materials. Prior to reasoning upon this fact, Mr. 

 Austen gives a very reasonable definition of the term " extraneous," 

 by which he understands that a fossil, or other body, is found in a 

 position not in accordance with its original habits, or the place of 

 its formation, as, for example, a " deep-sea mollusc amidst a number 

 of the inhabitants of shallow water," or a boulder of granite in a 

 chalk- or clay-deposit. This definition is sound and important, as 

 it points out to the palaeontologist the necessity of determining the 

 natural habitats of fossils, as well as their names, and to the geologist 

 the necessity of separating the extraneous from the native fossils, 

 before he can make a satisfactory comparison between the deposits 

 of different ages. Mr. Austen reviews the history of fragments of 

 " extraneous " rocks previously found in the Chalk, and then pro- 

 ceeds to draw the conclusions, which, though I have named them 

 speculative, I do not consider the less philosophical and important. 

 All the fragments he has noticed appear to have been water- worn, 

 and therefore must have been moved or acted upon by water. Some 

 of them exhibit marks of the Serpulce, &c, which attach themselves 

 to bodies resting for a time on the lower or quiescent portion of the 

 " marginal sea-belt," whilst others, more especially the smaller or 

 shingly kind, from their smooth surface, would appear to have 

 formed part of the upper portion, which, from its position, is 

 subject to the constant disturbance of the waves. D'Orbigny and 

 Edward Forbes, as quoted by Mr. Austen, were of opinion that the 

 pure white chalk was the deposit of a deep and open sea ; but Mr. 

 Austen shows, from the application of such reasoning as I have here 

 noticed, that every other form of sea-bed, from the abyssal to the 

 marginal, existed in the Cretaceous period. On the one hand, for 

 example, the presence of sand, gravel, and occasional boulders under 

 the circumstances detailed by Mr. Austen have proved the existence 

 of a marginal zone before the deposition of the upper portion of the 

 chalk ; and, on the other, the presence of forms of Bryozoa and of 

 other fossils which when alive must have been fixed at the base, 

 detached in the body of the chalk, show that such fossils are " ex- 

 traneous" in the position where they are found, and must have 

 vol. xrv, & 



