4 Calcareous Petrifaftians. [Book VL 



of this kind of matter from dropping waters, are 

 formed the large pendulous columns hanging like 

 icicles from the roofs and fides of caves. The moft 

 remarkable are in the Peak of Derbyfhire. Some- 

 times they are found in the arches of old bridges, and 

 arife from the water oozing through and carrying par- 

 ticles of lime with it. This earth fo concreted is called 

 ftalactites, ftone-icicles, or drop-ftone. 



5. The {hells of all cruftaceous animals, from the 

 coarfeft to the pearl which lines the {hell of the oyfter, 

 are all made up of this calcareous earth with a fmalj 

 quantity of animal gluten. Egg-lhells are of the fame 

 nature, and thofe marine bodies which, from their hard- 

 nefs and vegetable appearance, are called ftony plants, 

 fuch as are all the fpecies of coral, &c. 



Maries, which have been already mentioned as con- 

 taining calcareous earth, are generally divided into 

 three kinds. Firft, {hell- marie ; fccond, clay-marie j 

 third, ftone-marle. The firft is found in beds of con- 

 fiderable extent, and confifts of the remains of fea and 

 land {hells ; that which contains the fea {hells is com- 

 monly found in the greateft quantity. Of this kind 

 is that of Paris, mentioned by M. Reaumur, which is 

 about ten feet deep, and of great extent, confiding of 

 oyfter and other fea mells ; and foine very large beds 

 rnay be found in the neighbourhood of Woolwich. The 

 relics of land mells are thofe of fnails ; they have pro- 

 bably been carried by the current of fome wafer, and 

 depofited at one place, and the water being drained offj 

 the mells remained behind. Beds of frelh-water 

 Ihells are alfp found. Clay- marie is a calcareous 

 matter, which when expofed to the air crumbles to 

 duft ; it is to be diftinguiftied from common clay, by 

 effervefoing with acids., from the calcareous earth it; 



contains. 



