LOWER CHALK—MICROGRAPH10 STRUCTURE. 2(i l 
CHAPTER XXII. 
THE MICROGRAPHIC STRUCTURE OF THE BEDS 
FORMING THE ZONE OF AM. MARIANS. 
By W. Hill. 
Introductory Remarks. 
In the following pages it is proposed to give some account of the 
minute structure and contents of the successive zones of the Chalk 
as revealed by microscopic examination. Though much work 
has been done in the study of the Microzoa obtained from the Chalk 
of various localities and at different horizons, it was not till 1893, 
when Dr. Hume* published his Micro-Mineralogical Researches, 
that any systematic attempt was made to investigate the zonal 
distribution of those minute elements which constitute the greater 
part of the Chalk. In 1897 again, M. Caveuxt published a series 
of Monographs, in which he deals exhaustively with the lower 
beds of the Upper Cretaceous series in Belgium and with the 
zones of the Middle and Upper Chalk in the Paris Basin. 
Besides these two works little has been done, and the endeavour 
is now made to follow up this “ fruitful source ” of investigation 
as far as time and circumstances will permit. 
Methods.— Most of the details of the methods of these researches 
have already been given in a previous volume,! but it will perhaps 
be well to recapitulate them, and an explanation is also necessary 
as to the way in which the quantities of the various ingredients 
of the Chalk were estimated. 
1. The Examination of Thin Sections. —While little could be 
gained by the- study of thin sections of the Gault, much information 
can be obtained from the Chalk bv this means. In the course of 
many years’ work an extensive collection of thin sections has been 
made of specimens taken from all zones in the Chalk obtained from 
many localities between Devonshire on the west, Dover on the 
* Chemical and Micro-Mineralogical Researches on the Upper Cret. 
Zones of the South of England, by Dr. W. F. Hume. 
t Contribution a l’Etude Micrographique des Terrains Sedimentaires, 
by M. Cayeux. 
t Cretaceous Rocks of Britain, Yol. i. ; The Gault and Greensand, Mem. 
Geol. Survey (1900). 
4219. s 2 
