39 
excited, tell him, we have more tales of wonder in store ; of flocks 
of cattle, of large companies of men, and of even whole cities, with 
their inhabitants, converted to stone*. I could supply him, from 
a comparatively modern author, with an account of a troop of Spanish 
horsemen, who thus underwent the process of petrifaction f ; and 
with a very seriously attested relation of a petrified child, which was 
shown at Paris, and which was, occasionally, used by its possessor as 
a whet-stone + ! 
Yours. 
LETTER V. 
FORM OP THE EARTH’s SURFACE MOUNTAINS STRATA WIS- 
DOM MANIFESTED IN THEIR DISPOSITION DIFFERENT KINDS 
OF EARTHS ALUMINE ; FORMING CLAY, LITHOMARGA, SLATE, 
&C SILICA; FORMING ROCK CRYSTALS, CALCEDONY, FLINT, &C. 
LIME ; FORMING LIME-STONE, CHALK, TUFA, MARBLE, &C 
MAGNESIA ; FORMING STEATITES, ASBESTOS, SERPENTINE, &C 
SULPHURETS, PYRITES, OR MARCASITES. 
I MUST intrude on your patience, with one letter more of intro- 
ductory matter; it being necessary, before we speak of secondary 
fossils themselves, to give a cursory account of the matrices, in which 
* Aventini, lib. vii. Annal. Boiorum. Purchas’s Pilgrimage, p. 246. 
t Jos. Acosta, lib. iii. cap. 9. :|; Vide Helmont de Lithiasi. 
