12 
as ‘‘Ammonite zones,” yet that with increasing knowlelye 
of the range of specific forms such limits are purely 
arbitrary and may mislead,” a point for which I contended 
in my paper on the Lias, read at the Winter Meeting of 
the Warwickshire Naturalists’ and Archeologists’ Field 
Club, in February last. Mr. Day in an able paper on the 
Lias at Lyme, read at the British Association in Birming- 
ham, 1866, maintains the same views and brings forward 
the strongest arguments to corroborate them. The portion 
of this paper which more distinctly relates to the physical 
and economical Geology of the district under review is 
equally important, but it will be unnecessary to say more 
here than to state that the author conclusively shews that 
the barrier of the Mendip chain of hills has to a great 
extent modified the physical features of the whole line of 
country from Frome, through a great part of South Wales, 
and shut out the secondary deposits from the coal basin, 
within which unconformability very generally prevails ; 
the mountain limestone having been for a long period 
within the influence of the Liassic seas, and that from 
the latter have been derived most of the lead, iron, and 
calamine with which the mineral veins are charged. We 
might, perhaps, expect to find land and freshwater shells 
associated with insects in that portion of the lower Lias 
in which the annulosa most abound, but hitherto they 
have not been met with, though probably in some favoured 
spot, not yet searched, they will one day be discovered. 
Freshwater mollusks abound in some deposits, such as 
the Wealden, Purbecks, and Tertiaries, but terrestrial 
air-breathing shells are usually rare, being most numerous 
in the Bembridge (Kocene) limestone, in the Isle of Wight, 
and certain foreign Tertiary deposits about the same age. 
