OF THE NEIGHBOURHOOD. 21 



cavities are, however, productive of a very serious 

 inconvenience. They drain the rock so throughly, 

 that a well sunk in the limestone rarely produces 

 water. 



The organic reliques in the rock, which determine 

 its Geological character, are very numerous, and 

 considerably varied. Some of them have been fig- 

 ured in " Succinct account of the Plymouth Lime- 

 stone" published several years since by the Rev. 

 Richard Henneh, Chaplain of the Plymouth Citadel. 

 Since that period, he has added very extensively 

 to his collection of them ; and has sent an account 

 of them, with a catalogue, to the Geological Society. 

 To the scientific visitor, that Gentleman has pleasure 

 in exhibiting this collection ; which contains shells 

 of various kinds, bivalve as well as univalve; eu- 

 crinites, madreporites, and a long list of technical 

 names, not suited for a description of this kind. The 

 casual observer who may observe the face of our 

 limestone footpaths, when washed by the rain, will 

 not fail to observe elliptical and irregular blotches in 

 some of them, which, on nearer inspection, exhibit a 

 porous structure, the pores and fibres showing, by 

 their regularity their original connection with organ- 

 ised vitality. 



And if these rocks abound in organic reliques, 

 they present a no less extensive variety of crystal- 

 line form, in the groups which line some of the minor 

 cavities. The Rev. gentleman above cited, has not 

 neglected this part of their produce. His collection 

 contains some hundreds of specimens of calcareous 

 spar, in which, probably more than a hundred varie- 

 ties of form will be found ; and some others, not in 

 his possession, are known to have been found in 

 the quarries. 



It would perhaps be too much to expect that 

 these rocks should present us also with metallic 

 veins; and accordingly none such have hitherto 

 been found in them : nor, considering the great 

 extent to which they have been laid open, is it likely 

 that any are concealed. J. P. 



