EARTHS. ARGILLACEOUS. 33. CjEmentum. I2t 



arenaceoi Cinereous, connfting of di(iin£l granulations. 



Fumex cincrarius Sxf}. nat. xii. 3. /. 181. ». 5, 



Porusigncu*. Wall, fyjl, min. z^p.'i^'j^. n. i, 



Vo'canic fand. Kic-cvaTi mljier. i. ^.410. 



Volcanic r^nds. Thomfon chem. 4.. p. 150. 



Found in the ricighbourhood of Volcanos, and are compofed of 

 fmall hard grains varying in fize : they readily iir.k m water, 

 and aie ufually mixed with fmall fragments of feifpar, lava, 

 magnetic iron-flonc, Sec. they often cover a great extent of 

 ground, fometimcs to the extent of 50 leagues round the vol- 

 cano, and feveral feet thick. 



33. CMMENTllM, Confiding of iron, alumina, 

 a largc^r quantity of filica, and generailv a fmall 

 proportion of carbonate of lime : hardifh, light- 

 iili, porous, of an earthy texture, imbibing the 

 water in vvhicli it is immerfid w'th a hifllng 

 noife, crackling u'hen dried and prefled with the 

 thumb, rough, without lufhre: when powdered 

 and beat up with water and quicklime becoaang 

 fo hard as not to be penetrated by water, eafiiy 

 melting in the fire into a black fcoria. 



Tufa* CoUefted into entire clifFj. and vaft flrata about volcanic 



mountains, of a common form. 



Giosni lito'o^. Fi^fu^vian. p. I 74, 



Tufas. Kir-zvan mineral. \ . p. ji^i^. 



TnfFwacke. Schmeijjey mineraU I. p. 187. 



Found in the neighbourhood of volcanos, particularly in Italji 

 about KopJes and Romey and confills of compaft mafl'es of 

 pouzzolano, find, flaggs, pumice, and other iton^s of vol- 

 canic origin: colour njoftly fmoke- colour, cinereous, blackifli, 

 brown, cchraceous, yellowifh-grey, cr brownifli yellow, 

 rarely reddifh, greenifh or variegated : it is commonly mag- 

 netic, of an earthy fradure, and not eafily decompofed by the 

 aclion of the air; fometimes it has a fmall mixture ot bon-s, 

 ihells and other calcareous fubitances, and then effervefces a 

 little with acids. 



Forming large ftrata under the furface of the common foil, 

 of a common form. 

 Crementum induratam. Cronst. miner. 207. «. 8. 2, 

 C^ementum induratum. IVall./yst. min» i./. 97. «. 2, 

 Trafs or Terras. Kir^van mrreral. i. /, 4r3. 

 Trafs or Tarnis. SchmeiJJcr mineral, i. /. 187. 



YOU vr. — CL 



