LOWER CHALK—MICROGRAPHIC STRUCTURE. 
313 
w'halk and the whiter rock which immediately surrounds such 
patches, the Rev. W. R. Andrews, at our request, kindly forwarded 
to us examples from Eastbourne. 
The results of our examination show that the bluish-grey chalk 
contained a larger proportion both of fine and coarse residue 
than the whiter. 
In the bluish-grey example ITS per cent, of coarse residue was 
separated from the clay (nearly half of this was the green matter 
described above), there were a very few glauconitic grains, 
the remainder was foraminiferal debris and sponge-spicules. In 
the whiter chalk only - 20 percent, of coarse residue was separated, 
nine-tenths of which was foraminiferal debris with some sponge- 
spicules ; the remainder consisted of small masses of porous iron 
oxide, with only one or two grains of glauconite. The Foramini- 
fera isolated from the two samples were identical, and in neither 
were there free quartz-grains of any size. 
The clay separated was rather dark grey in the bluish, and 
grey inclining to a brownish tint in the whiter chalk. While 
washing the latter a kind of heavy flocculeiit matter was 
observed, which settled quickly and doubtless carried with it some 
of those finer particles which would otherwise have remained 
with the coarse residue. 
Thus, it seems, the chief difference in these two samples is the 
presence of green matter in the bluish-grey chalk and its absence 
in the whiter. 
The difference in the weight of the fine residue is remarkable 
in a deposit otherwise resembling each other. Can it be that 
in the whiter chalk the green matter has become oxidized, and 
that the salts of iron so formed have been removed by percolating 
water ? 
Though the green matter seen in the coarse residue was in small 
lumps, yet it may be distributed through the chalk in particles too 
small for separation. We have, however, been unable to detect it. 
Tabulation of Results. 
Appended will be found a table of the results of the analysis of 
sixteen specimens of the chalk of this zone from various localities 
and horizons. We are indebted to Mr. H. B. Woodward, for 
sending the two specimens from the Isle of Wight, and to the 
Rev. W. R. Andrews for two samples from near Eastbourne, The 
remainder are of our own collecting : — 
