1857.] GODWIN-AUSTEN BOULDER IN CHALK. 257 



workmen to raise off the chalk with a pick : in doing this, some of 

 the sand separated with the raised chalk ; but the principal portion 

 remained, and showed that at one part it had been in close juxta- 

 position with the block, and that it ended abruptly in the chalk at 

 the opposite end of its mass ; in this sand there was a fragment of 

 greenstone much decomposed, and which has since fallen to pieces. 



From the account of the workmen, and from what I saw, as well 

 as from the materials which have been preserved, it is clear that, 

 together with the larger granitic boulder, there was also a collection 

 of blocks of smaller dimensions ; and all these were also water-worn. 

 Most of them were composed of a peculiar and very different rock, 

 consisting of augite, with tabular double crystals of felspar, such as 

 might be called a melaphyre or porphyritic augite : the largest of 

 these, from the portions which remain, must have been of consider- 

 able size, weighing as much as twenty to twenty-five pounds, but, in 

 common with all the other specimens of the same rock, it was much 

 decomposed ; there was a central portion which was only partially 

 so, and from which the compact specimens now exhibited were 

 derived : the smaller pebbles were wholly decomposed, and readily 

 fell to pieces, forming a sharp sand. Most of the loose material 

 lying on the floor of the quarry, where the blocks had been broken 

 up, consisted of this decomposed greenstone, but which, from the 

 iron in the original rock, was of a browner colour, and had not been 

 derived from the larger granitic boulder. 



In the specimen of greenstone from this spot, which I myself found, 

 it was clear that the process of decomposition, with respect to these 

 fragments, had been subsequent to inclusion, as, in their decomposed 

 condition, they could not have been rounded as we there found them. 



In addition to these large portions of rock, there was also a com- 

 pact mass of siliceous sand. Some of this had been thrown aside as of 

 no interest ;• but a portion was still in situ, and included a small de- 

 composed fragment of greenstone : when the sand was broken down, 

 this last so fell to pieces and mixed itself with it, that it was natural 

 that a casual observer should have supposed, first, that these crystal- 

 line rocks were all alike in composition, or granitic, and, next, that 

 the finer materials were only its decomposed portions. 



An examination of this portion of the mass of materials will be 

 sufficient to establish that it is fine water-worn beach-sand, derived 

 from the waste of a coast-line of some crystalline rocks. 



Observations and Inferences, — Referring to the whole suite of 

 smaller rock-specimens from the White Chalk which have been met 

 with from all quarters, we may determine thus far, that, in respect 

 of form or condition they have this in common with the larger speci- 

 mens from Purley, they are all water-worn, either in the form of 

 shingle or rounded boulders, — that, as regards their mineral cha- 

 racter, they have been derived largely from granitic and greenstone 

 masses ; whilst they differ in this, that they have occurred as isolated 

 blocks or pebbles*, with the exception of those of Houghton (Sussex), 

 where they were met with scattered over the same level or sea-floor. 



* M. Deslongchamps, of Caen, pointed out many years since, that modern Cro- 

 codiles are in the habit of swallowing pebbles ; and he suggested that certain 



