185/.] GODWIN-AUSTEN BOULDER IN CHALK. 255 



others the property of Mr. W. Harris. These were interesting, as, 

 in addition to the crystalline rock-pebbles, there are some small spe- 

 cimens which have the appearance of being volcanic scoriae. Dr. 

 Forbes Young also kindly communicated some facts relating to the 

 Purley discovery, and placed at the disposal of the Society the seve- 

 ral materials which he had collected at the pit ; the largest frag- 

 ment measures about 12 inches in each of its two longest diameters, 

 and weighs upwards of 24 pounds. 



Mr. Catt's collection contains three specimens of rather soft, 

 marly, micaceous sandstone, of a greenish-grey colour, one pebble 

 of opake quartz, two of transparent quartz, and one of coloured 

 quartz : these are all small. There is a much larger sub-rhomboidal 

 fragment of dark clay-slate, with the angles rounded, and lastly, a 

 block of fine-grained sandstone (quartzite), weighing thirteen pounds 

 fourteen ounces. All these fragments have been derived from old 

 sedimentary (palaeozoic) strata. 



The largest block shows the bases of several attached bodies, such 

 as Diblasus or Isis, a Serpula, a Bryozoon (Diastopora ramosa ?), 

 and the lower valve of a Spondylus lineatus. This block had been 

 rolled about on a beach, after these forms had attached themselves. 



Mr. Cunnington's specimen consists of a fragment of thin fissile 

 slate (very like common roofing-slate) imbedded in a chalk-flint. 

 The slate has apparently been broken in the direction of the cleavage, 

 and at the time when the flint was broken, so that the original form 

 of this fragment cannot be determined. 



As the cases where the occurrence of such materials has been 

 observed are likely to be far less numerous than those which have 

 escaped observation, or not been recorded, and as the pits where chalk 

 is quarried present only a most trifling portion of its mass when com- 

 pared with the horizontal extent of that formation, we may fairly 

 infer that the differences of such extraneous materials must be much 

 greater than we have heretofore supposed. 



Form of the Boulder. — When I visited the Purley chalk-pit, I was 

 informed that the large block had been still further broken up at 

 the time of Dr. Young's visit, so that the destruction of the principal 

 mass was then almost complete ; some portions had been carried 

 away by various persons, whilst others had been put into the kiln, 

 by way of experiment, for the purpose of ascertaining whether they 

 would burn into lime, like the chalk. The largest fragment which 

 I was able to secure rather exceeded five pounds in weight. 



On the spot where the blocks had been broken up, I found a con- 

 siderable quantity of loose fragmentary materials identical with one 

 of the larger portions, and derived from the more decomposed parts. 



According to the account given by the quarrymen, the block, 

 when first exposed, presented a rounded surface, — a statement 

 which is confirmed by the appearance of all the fragments which 

 have been preserved, which also show it to have been boldly eg°-- 

 shaped. When I first visited the quarry, I was told that the cavity 

 (or the lower part of it) which the block had occupied remained in 

 the same condition as when it was first lifted out of it. On carefully 

 removing the loose chalk that had fallen in, there was presented a 



