Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/178

 of its fossils, and the absolute sameness of its general features, will no longer permit us to describe by a distinct name, this important formation.

It need not excite any surprize to find the floetz trap incumbent on a bed of such recent formation, since in the north of Italy it may be seen to rest upon strata still less ancient, and analogous to those which occur in the basins of London and of Paris.

The Irish chalk is seldom of a texture sufficiently loose to soil the hand, and in the few instances where this does take place, it is in a very slight degree: its general colour is either perfect white, or white with a very slight tinge of yellow; towards the lower beds it passes into an uniform ash colour, the texture then becomes still more compact. It is sometimes traversed by slender veins of calcareous spar, these are more frequent in the lower beds: it contains (though in very small quantity) kidney shaped nodules of iron pyrites; but the most striking of its imbedded contents are the flinty nodules which traverse the mass in regular horizontal strata, distant from each other, by an average interval, about two feet and a half; the flints cease in the lowest beds. Among the flints some of remarkable size, and of a regular and apparently organic figure occur; these are known by the name of Paramoudra, and are also found in the chalk of Norfolk. It is superfluous to describe farther the characters of these beds of flinty nodules than by saying, that they are precisely the same with those presented in every English chalk pit.

The average thickness of the chalk formation in Ireland may be estimated at between two and three hundred feet; the upper beds seem to have been partially redissolved before the basaltic mass was deposited upon them, since along the line of junction a confused aggregation of chalk flints exists, imbedded in the