LOWER CHALK—GENERAL ACCOUNT. 
11 
CHAPTER II. 
GENERAL ACCOUNT OF THE LOWER CHALK. 
Definition and Limitation. 
It is only within the last twenty years that what is now termed 
the Lower Chalk has taken rank as a definite stage in the Upper 
Cretaceous Series. In the earlier part of last century the name was 
used in a more or less indefinite manner for the lower part of the 
white chalk, excluding the Chalk Marl. After the discovery of 
the “ Chalk Rock ” by Mr. Whitaker in 1859, the term was used 
in Survey Memoirs, and in text-books published between the years 
1860 and 1870, for the chalk which lay between that rock and the 
Chalk Marl. 
In 1870 Mr. Caleb Evans made a more rational use of the term by 
proposing to include in it the Chalk Marl, but he still included some 
beds which are now referred to the Middle Chalk (see p. 6). 
In 1876 Dr. Charles Barrois described the Chalk of England on 
the basis of the classification which had been worked out in France, 
and showed that the separation of the Turonian from the Ceno¬ 
manian was very clearly marked throughout the south of England. 
English geologists, however, were not at that time prepared to 
accept the French scheme of nomenclature, and it was not till 1880, 
after the mapping of the country round Cambridge and the dis¬ 
covery of the Melbourn Rock, that the limits of the Lower Chalk 
were defined in a manner that could be adopted by the Geological 
Survey. This definition was published in the Geological Maga¬ 
zine (1880) and in the Survey Memoir on “ The Neighbourhood of 
Cambridge ” (1881). 
In that memoir the zone of Belemnitella plena was included in 
the Melbourn Rock, because in Cambridgeshire and Hertfordshire 
it includes a medial band of hard rock ; but a subsequent study of 
these beds* led to the separation of the Belemnite marls and their 
inclusion in the Lower Chalk. The plane of separation thus drawn 
was identical with that taken by Dr. Barrois as separating the 
Turonian and Cenomanian. 
Beds included tn Lower Chalk. 
As now defined, therefore, the Lower Chalk includes all the beds of 
marl and chalk which lie between the highest bed of Gault or Green-, 
sand and the Melbourn Rock, which is the base of the Middle 
* On the Melbourn Rock and the Zone.of Belemnitella plena, .by W. Hill 
and A. J. Jukes--Browne. Quart. Journ.'Geol. Soc., Vol. xlii. p/216, 1886. 
