FLCETZ ROCKS. 7. The porphyritic ftone refembles clay-porphy- ry, but is much more earthy, and the cryftais of felfpar are few, fmall, and fomewhat earthy. C>uartz occurs but feldom. The bafis of the ftone is frequently marked with green fpots; it is fometimes amygdaloidal, and contains, befides other foffils, chalcedony. It occurs in beds of confiderable thicknefs. It may be confidered as a member of the porphyry fuite, and may be deno minated the Third Porphyry Formation. 8. The locks of this formation are very diftindly ftratified . the coal is alfo fometimes ftratified ; but it occurs more generally in beds; and thefe are from a few inches to feveral fathoms thick. Fre quently many beds of coal occur in the lame de- poiition, a charader which diftinguflhes this for mation from that in the neweft fioetz-trap, where the beds ufually occur fingle, and of great thick nefs. 9. It never rifes into mountains, but generally forms hilly country ; and thefe hills are fometimes very low and flat, and graduate into flat coun try ; and fuch trads are traverfed by narrow and deep valleys, which prefent hanging diffs and mu ral precipices. jo. It is fometimes fituated in ravines, or in ba- fin-flfaped hollows, or at the foot of mountain groupes. In this country and Weftphalia, the coal formation extends over confiderable trads of country, fometimes filling immenfe bairns, in other cafes
