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LOWER CHALK—MICROGRAPHIC STRUCTURE 263 
The results obtained by this method of investigation will be found 
in the tables appended to the description of each zone. The arrange¬ 
ment is as follows :-—(!) Each specimen is numbered and its 
locality indicated. (2) The amount of the material taken follows, 
and then (3) the percentage soluble in the acid. Then follows (4) 
the percentage of the coarse, and (5) of the fine residue, and 
(6) the total quantity of each, with (7) its colour. 
The composition of the coarse residue is then given with (1) the 
names of such detrital minerals as have been recognised, their 
percentage and the maximum and average size of the grains. 
(2) The secondary minerals follow, but dimensions of the glauconitic 
grains only are given ; then come (3) the generic names of such 
Foraminifera as were isolated in the acid residues, and their 
percentage; the final column (4) being given to shell fragments 
and particles whose identity is uncertain. Finally, remarks in 
each case draw attention to any peculiarity seen in the residue; and 
in brackets are given the leading characteristics of the specimen 
when seen as a thin section, with the estimated percentage of the 
recognisable organic ingredients. 
The zonal divisions followed are those described in the earlier 
pages of this volume. It is very necessary in considering the chemi¬ 
cal and micro-mineralogical characters of the various zones to indi¬ 
cate as nearly as possible the horizon from whence the specimen 
comes. It will be seen in the sequel that there are very con¬ 
siderable lateral as well as vertical differences, and the approxi¬ 
mate distance in feet above or below some well-marked bed should 
always be given if possible. 
3. Washings. — Many specimens of the softer chalks were washed 
in water without acid, the finer part removed by levigation, and 
the chief characters of the coarse particles which remained behind 
noted. These included Foraminifera, valves of Ostracods, frag¬ 
ments of shell, spines of Echinoderms, &c. These particulars are 
given under the head of “ Washings.” 
Dr. Hume has very kindly put into our hands the results of 
some further investigations of chalks from Devonshire and the 
Midlands, which he has had no opportunity to complete. These 
we have incorporated, but have kept his work separate as far 
as practicable. 
We have also drawn freely from Dr. Hume’s published account 
of the micro-mineralogical aspect of the Chalk. Our best thanks 
are due to him for giving us all the information in his power of 
the way in which he has carried on this work. 
Mr. J. J. H. Teall, kindly undertook to examine our residues, 
and to report on the detrital minerals, and Mr. F. Chapman to 
name the Foraminifera isolated in the residues and washings. 
To bpth these gentlemen our best thanks are also due. 
