254 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 1G, 



I accordingly invited my friend Dr. J. Forbes Young to accompany 

 me to the place, which he did. 



" We set the men to work round the spot ; and they found at the 

 bottom a quantity of coarse sand-like materials, which on examination 

 proved to be decomposed rock of the same kind. They also dug 

 from the same place several large fragments of greenstone in a 

 state of decomposition and surrounded by debris of their own class." 



It was after this, and some time in the month of August, that I 

 received a communication from my friend Mr. Rupert Jones, re- 

 specting the discovery in question. I lost no time in visiting the 

 locality indicated ; and from what I then saw, as well as from the 

 evidence I collected, I felt perfectly satisfied that the boulder, together 

 with its associated materials, when first discovered, was fairly im- 

 bedded in the solid chalk, and that their mode of occurrence was 

 suggestive of various considerations deserving of notice. 



Previous notices of extraneous materials in Chalk. — Though 

 I cannot find that the occurrence of such materials as these has 

 ever been made the subject of any special communication to this 

 or any other like Society, yet it must not be understood that ex- 

 traneous materials in the body of the White Chalk formation have 

 not been noticed. I have several times had such specimens brought 

 to me ; they are also to be met with in numerous private collections ; 

 and some of them I am enabled to exhibit here this evening, through 

 the kindness of their possessors*. 



Major-Gen. Portlock has noticed several remarkable examples of 

 blocks of hard black basalt, isolated in the Chalk of Ireland (see 

 ' Report on Londonderry/ &c, pp. 93, 94). In 1840, Mr. Griffith 

 also called attention to the occurrence of flattened spheroids of 

 syenite in the Chalk of Antrim. 



There are also two other short recorded notices. "In this countiy," 

 observes Dr. Mantell ('Geology of the S.E. of England,' p. 78), "the 

 Chalk very rarely contains traces of older deposits. The only instances 

 of extraneous rocks that have come under my observation are pebbles 

 of quartz, and some fragments of green schist/' 



Mr. Dixon (' Geology of Sussex,' p. 69) says, " Small pebbles and 

 large rolled fragments of sandstone and quartz-rock are occasionally 

 discovered in the centre of the Upper Chalk. Mr. Coombe found one 

 specimen weighing near fourteen pounds at Houghton, Sussex; and I 

 have seen others from the same pit of two and three pounds weight ; 

 several also have been sent me by Mr. Catt from the pits near Lewes." 



Description of the specimens exhibited. — I may here observe, that 

 shortly after the published notice of the verbal communication I made 

 of the Purley discovery to the Geological Section of the British Asso- 

 ciation at Dublin, I was informed by Mr. W. Cunnington, of Devizes, 

 that a specimen of slate imbedded in flint had been found in Wilt- 

 shire. I had next an opportunity of examining a collection of 

 extraneous materials from the Chalk, belonging to this Society, and 



* Specimens from the Museum of the Geological Society, and from the Collec- 

 tions of the Rev. T. Wiltshire, F.G.S., W. Cunnington, Esq., F.G.S., W. Harris, 

 Esq., F.G.S., and H. Catt, Esq., were exhibited when the paper was read. 



