50 



their form and structure to be much more easily traced 

 than in the chalk itself. The most common forms in which 

 these occur are oblong or nearly globular : and they are 

 either imbedded in the chalk, or scattered on its surface, 

 or in the neighbouring declivities. These may be frequently 

 found on the Sussex Downs, the Gogmagog Hills of Cam- 

 bridgeshire, and, indeed, on or about most of the chalk 

 hills. These nodules appear to have been formed round 

 fragments of sponge of different forms and structure, and to 

 be more or less filled, according to the degree of decom- 

 position and subsequent removal which the included sub- 

 stance had sustained after its inclusion. In some spe- 

 cimens, particularly among those of Wiltshire, which have 

 been collected by the liberal encouragement of ]Miss Benett, 

 a tuberous or ramified body, and, in some instances, two 

 such bodies, are extended across the cavity of the flint, and 

 covered over with a fine white powder of chalk and silex 

 blended. These bodies appear to be casts in the cavities 

 of sponge, the substance of which has passed away. In 

 others the substance which had been included appears to 

 have been broken down and removed, and its place occupied 

 by chalk which has intruded in a pulverulent state ; whilst 

 in others the cavity alone remains. Oblong nodules, found 

 on Stokenchurch Hill, and for some distance on the Oxford- 

 shire side, very frequently exhibit specimens, which, on 

 being broken, display the structure of the Zoophyte in great 

 distinctness. In the chalk marl at the foot of the cliff at 

 Beechey Head, are botryoidal and lamelliform masses, 

 which, not only from their external forms, but the appear- 

 ances yielded on their fracture, lead us to the recollection 

 of the masses of fossil sponge at Farringdon, and which, in 

 all probability, have been yielded by the chalk marl. 



Fossil sponge of a very fine texture, and in a pulvinated 

 form, Is sometimes found investing the shells accumulated 

 in the cliffs at Walton and Harwich. 



