MIDDLE CHALK—MICROSCOPIC STRUCTURE. 
505 
A considerable portion of many of the residues consisted of 
small aggregations apparently of fine siliceous matter; these had 
no definite form, and did not appear to be fragments of 
Foraminifera. 
Foraminifera. —Our remarks on the Foraminifera of the 
Melbourn Rock are confined exclusively to the forms isolated from 
the acid residues; doubtless if time allowed, and a sufficient 
number of specimens were broken up and examined, the list of 
forms would be materially increased. This list is as follows: — 
■i 
Mupe Bay. 
' : 
Swanage. 
Dover. 
Hitchin. 
Ringstead, 
Hunstanton. 
Louth, Lines. 
Speeton, 
Yorks. 
Rhizammina - - 
7 
7 
Reopliax (sp. nov.) - 
- 
— 
- 
X 
— 
— 
Haplophragmium sp. 
- 
H 
H 
- 
— 
— 
— 
Ammodiscus incertus, d'Orb. - 
X 
H 
X 
X 
X 
X 
X 
„ tenuis Brady 
X 
- 
- 
— 
X 
- 
X 
,, charoides J. k P. 
— 
— 
X 
X 
X 
— 
— 
Textularia minuta, Berth 
— 
H 
— 
— 
— 
— 
— 
Bulimina Presli Beuss 
X 
— 
X 
X 
— 
— 
— 
,, affinis, d'Orb. - 
— 
— 
— 
— 
— 
— 
„ brevis, d'Orb. 
— 
X 
X 
— 
— 
Those marked H are recorded in Chemical Micro-Mineralogical Researches, 
pp. 47 and 50 ; the remainder are from our own residues, and have been 
identified by Mr. F. Chapman. 
It will be seen that the prevailing forms of this zone belong to 
the genus Ammodiscus. Bulimines occur sparingly ; Bulimina 
Presli and Bulimina brevis continue into this zone, but the speci¬ 
mens are small and delicate. It may be noted that they still 
occur in southern specimens. All the forms in the above list 
range up from the Lower Chalk. 
The tabulated results obtained from analyses of the Melbourn 
Bock will be found on p. 512. 
B. Chalk above Melbourn Bock. 
Microscopic Aspect. 
With one exception there seems but little difference in the 
chalk of this zone; from whatever locality the specimen is taken 
the same general characters are exhibited when a thin section 
is viewed under the microscope. 
This chalk is specially characterised by the abundance of 
Spheres, winch seem larger and more boldl} 7 outlined than at 
any other horizon : their cell-walls are often well defined by 
a rim of clear crystalline calcite, and their interiors are filled with 
