Trap Boulders in the Diluvium of Essex. 145 



its hind legs. But it has since occurred to me that that 

 shortness may be owing to some accident; for the late Lans- 

 down Guilding, in the hinncean Transactions, has informed 

 us that, "if it loses a leg by violence, this is reproduced, but 

 of a smaller size, at the next change of skin" (my Synopsis, 

 p. 11.); hence it is not improbable that this accident might 

 have happened to the specimen which I examined. This re- 

 production is well known to occur with crabs and lobsters, 

 and also with spiders. 



An example of this phenomenon is well shown by a speci- 

 men of Diapherodes, contained in the Linnaean Society's col- 

 lection ; which has one of its hind legs short, while the other 

 is of the natural size ; proving, in this case, that one leg only 

 was injured, and renewed on change of skin. 



Acanthoderus scabrosus (p. 14-.) I now believe (from a 

 specimen kindly lent me by Mr. Templeton, brought from 

 the Isle of France) to be the larva of a winged species, which 

 has not yet been discovered in its perfect state. Acantho- 

 derus Dumerilii, and even A. spinosus (p. 14.), with Bacteria 

 fragilis, acaenosa (p. 18.), and spinosa (p. 43.), may probably 

 prove to be only larvae. 



I have offered these suggestions for the purpose of calling 

 the attention of entomologists to an examination of the doubt- 

 ful points, and, at the same time, to correct these supposed 

 errors in my Synopsis of the family. 



Art. VIII. Observations upon the Boulders of Trap Rocks, $?c, 

 which occur in the Diluvium of Essex. By J. Brown, Esq., 

 RG.S. 



In the Magazine of Natural History, Vol. VIII. p. 349, 

 350., there is a synoptical tnble of the boulders of trap rocks, 

 porphyries, granite, &c, which have been found in the gravel 

 at Stanway, and other places within a radius of fifteen miles, 

 in the county of Essex. 



It is well known, that all rocks recognised by the above 

 terms, from possessing characters peculiarly their own, and 

 which are found, in some parts of the world, occupying exten- 

 sive tracts of country, are of an igneous, or volcanic, origin. 



But, although this fact is familiar to those who make this 

 subject their study, it is not commonly known to persons in 

 general, that the gravel which is used every day in repairing 

 our common roads, and which is spread over a large portion 

 of this and the adjoining counties of Suffolk and Norfolk, to 

 a considerable depth, is in part, and in some localities largely, 



Vol. I. — No. 3. N. s. m 



