1857.] GODWIN-AUSTEN — BOULDER IN CHALK. 253 



sedimentary strata of the earth's crust has produced a complete 

 change in such views ; the remains of animals, such as Mollusca, are 

 inseparably connected with the deposits formed beneath the areas 

 of water in which they lived. 



Materials, whether organic or inorganic, can be said to be "ex- 

 traneous" only with reference to the special conditions of accumulation 

 implied by the beds in which such materials occur. A. solitary deep- 

 sea mollusc amidst an assemblage of shallow-water forms is an 

 " extraneous " one ; and, on the other hand, the boulders and shingle 

 of a coast-line, or ponderous shells from the marginal zone, are 

 foreign to deep-sea sedimentary beds. Such is the sense in which 

 the term "extraneous" has been employed in the following pages. 



Whenever, in the examination of old sea-beds, such phenomena 

 as these present themselves to the geologist, their investigation will 

 be attended with interest and advantage : the solution of such ano- 

 malies invariably conducts to some further knowledge of the conditions 

 and agencies of the period when such things happened. 



The evidences of abnormal agency are to be met with in the sedi- 

 mentary deposits of all periods. 



Locality and Position of the Croydon Boulder. — The Boulder 

 which, together with some other associated materials, forms the sub- 

 ject of the present communication was found in a chalk pit, worked 

 by Mr. Pettiver, by the side of the old London and Brighton road, 

 near Purley, about two miles south of Croydon. 



The road at this place runs along a deep valley in the chalk ; and 

 it may be here observed that the upper and higher surface of the 

 adjacent district is much eroded into furrows and covered with 

 detritus, but that the sides of the valley are altogether free from 

 either. The valley is one of those which have been excavated since 

 the removal of the lower tertiary strata from off the district. The 

 bottom of the valley is filled with a thick accumulation of gravel, 

 being an extension of that which is to be seen near the Croydon 

 Station, but which gravel does not rise to the level of the floor of the 

 quarry where the boulder was found. 



The portion of the Chalk-formation in which the pit is worked, is 

 the lower part of that containing flints. 



The boulder in question was originally discovered by the men 

 employed in the quarry, who exposed it in raising chalk for lime ; 

 it was removed and put aside, but the place it had occupied would 

 not seem to have been much disturbed. The first person to whom 

 it was subsequently shown was Mr. Simmonds, who, judging from its 

 external ochreous appearance, took it for a huge nodule of iron- 

 pyrites. He accordingly recommended the men to break it, when, 

 to his astonishment, he found it to be a mass of crystalline rock 

 resembling granite. 



In an account of the discovery, lately communicated to Mr. Rupert 

 Jones, Mr. Simmonds says : " Thinking it sufficiently interesting, and 

 never having seen anything of the kind myself after considerable 

 experience in the Chalk, I thought it right that others should be 

 witnesses of the fact whilst the hole from whence it came was open. 



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