ITALY. LETTER XVIII. 259 



LETTER XVIII. 



Florence, May 14, 1772. 



ON the road from Siena to this place, I 

 obferved the following varieties of the 

 ground. 



Near the Florentine-gate hills of common 

 coarfe gritty brown- reddifh fea-fand, either loofe 

 and incoherent, or hardened into arenaceous 

 ilone. A finer and yellow variety of it appears 

 beginning on the other fide of the city near the 

 Roman gate. I believe I have obferved, that this 

 fand and thefe fand-ftones are fuperincumbent on 

 the before-mentioned marl-hills, which I noticed 

 between Radicofani and Siena. I obferved in this 

 fand and fand-ftone beds, the following fmaller or 

 thinner flrata and mixtures, which fucceeded or 

 followed without any order, a. Now and then a 

 ftratum of grey limeftone, inclofmg b. A thin bed 

 of oblong and fmall oyfter-fhelk, of the fame 

 fpecies, and nearly refembling the oyfters in Gual- 

 S 2 tiqrj 



