GENERAL ACCOUNT OF THE CHALK. 5 
the horizon of the Chalk Eock. Both S. Woodward and his friend 
C. B. Bose* * * § drew special attention to the important fact that the 
several divisions of the Chalk contained different assemblages of 
fossils. 
As time went on this fact impressed itself on the collectors of 
Chalk fossils, so that in 1853 Mr. Sharpe recognised the necessity 
of recording the general stratigraphical positions of the fossils he 
described, but found himself obliged to be contented “ with referring 
specimens to one or other of the following great divisions of the 
Chalk, which are easily recognised, although they are not separated 
by any well-defined lines/’ f His divisions are : — 
1. Upper Chalk (Norfolk, Gravesend and Northfieet). 
2. Middle Chalk, which contains but few fossils. 
* . • / 
3. Lower or Grey Chalk, containing numerous fossils. 
He places the Chloritic Marl at the base, and includes the Chalk 
Marl in the Lower Chalk. His Middle Chalk is completely unde¬ 
fined, as he refers to no sections, and the only fossils he refers to it 
are Belemnitella quadrata, Ammonites per ampins, Am. bravai- 
sia/nus and Am. Woolgari —fossils which really occur at widely 
distant horizons. 
The first real advance toward a definite subdivision of the Chalk 
was made by W. Whitaker in 1859,^ who then described the Chalk 
Eock, and defined it as the topmost bed of the Lower Chalk, in 
Wiltshire, Berkshire, and Oxfordshire. He remarks that “ where- 
ever the Chalk-rock has been seen in the above-mentioned country 
it forms an exact boundary between the Chalk with flints and the 
Chalk without flints.” In 1865 the same observer determined 
the true position of the Totternhoe Stone, and distinguished the 
following subdivisions in the Chalk of Buckinghamshire : — 
Clialk with flints 
Chalk Rock 
Chalk with few flints 
Chalk without flints 
Totternhoe Stone 
Totternhoe Marl 
/ hard and bedded § 
Iblocky and marly 
= Upper Chalk, 
l Lower Chalk. 
} Chalk Marl. 
He found that these horizons could be followed for a long distance, 
and the outcrop of the Totternhoe Stone was engraved on one of the 
Geological Survey maps (46 S.W.), but no attempt was then made 
to estimate the range of the fossils in these subdivisions. 
* A Sketch of the Geology of West Norfolk, by C. B. Rose. Phil. Mag., 
Ser. 3, Vol. vii. pp. 171, 274, 370, and Vol. viii. p. 28 (1835-1836). 
f Fossil Mollusca of the Chalk, Pal. Soc. Introduction, 
t Catalogue of the Rock-specimens in the Museum of Practical Geology, 
Ed. 2, 1859, p. 296. See also Quart. Journ. Geol. Soc., Vol. xvii, p. 166. 
§ This appears to have included the rocky chalk which is now known 
as the Melbourn Rock. 
