646 PHILOSOPHICAL TRANSACTIONS. [anNO I67I, 



to animals, has been dissolved or wasted by the penetrating force of juices, and 

 that a stony substance is come in tlie place thereof,) but that these cockle-like 

 stones ever were, as they are at present, lapides sui generis, and never any part 

 of an animal. That they are so at present, is in effect confessed by Steno in the 

 above cited page; and it is most certain, that our English quarry-shells have no 

 parts of a different texture from the rock or quarry where they are taken, that 

 is, that there is no such thing as shell in these resemblances of shells, but that 

 iron-stone cockles are all iron-stone; lime or marble all lime-stone and marble; 

 spar or crystalline-shells all spar, &c. and that they never were any part of an 

 animal. My reason is, that quarries, of different stone yield us quite different 

 sorts or species of shells, not only one from another (as those cockle-stones of 

 the iron-stone quarries of Adderton in Yorkshire differ from those found in the 

 lead mines of the neighbouring mountains, and both these from that cockle- 

 quarry of Wansford bridge in Northamptonshire, and all three from those to be 

 found in the quarries about Gunthrope and Belvoir Castle, &c. ;) but, I dare 

 boldly say, from any thing in nature besides, that either the land, salt, or fresh 

 water does yield us. It is true, that I have picked out of that one quarry of 

 Wansford very resemblances of murices, telinse, turbines, cochleae, &c. and yet I 

 am not convinced, when I particularly examined some of our English shores for 

 shells, also the fresh waters a,nd the fields, that I did ever meet with (N. B.) 

 any one of those species of shells any where else, but in their respective quarries, 

 whence I conclude them lapides sui generis, and that they were not cast in any 

 animal mould, whose species or race is yet to be found in being at this day. 



Further Communications about Vegetable Excrescences, and Ichneumon 

 Worms. By Mr. Lister, N" 76, p. 2284. 



See the preceding observations on similar subjects, of which this is a kind 

 of continuation. 



An Account of some Books. N° 76, p- 2286. 



I. Johannis Wallisii, S. Th. D. Geometriaa Professoris in Academia 

 Oxoniensi, Tractatus de Motu Pars III. An. 1671, in 4to. 



In this third and last part, the excellent author, continuing his doctrine of 

 motion, treats, amongst other things, of the five mechanical powers, or noted 

 engines for the facilitation of motion. There are also described six sev^eral forms 

 of flat roofs, for large rooms, framed of short timbers, much shorter than the 

 breadth of the room, mutually supporting one another : with methods of com- 

 puting the weight sustained by every joint. Of several sorts of winchers^ 



