C H A 



on the north coast. The chalk 

 formation is composed of six di- 

 visions, namely, 1. The Maestricht 

 beds; 2. The upper chalk with 

 flints; 3. The lower chalk without 

 flints ; 4. The Upper green sand ; 

 5. The gault ; 6. The lower green 

 sand. Some authors divide the 

 chalk formation differently, con- 

 stituting the grey marl, which lies 

 between the chalk without flints, 

 above, and the firestone, or upper 

 green sand, below, a distinct mem- 

 ber. Others separate the green 

 sand formation from the chalk 

 formation, making the chalk marl 

 the lowest member of the chalk 

 formation, and placing the upper 

 green sand, or firestone, the gault, 

 and the lower green sand, in the 

 green sand formation. The whole 

 of these are marine deposits. It 

 must however be kept in mind that 

 this order is far from constant. 

 The members of the cretaceous 

 group are ranked as the last of the 

 secondary period; and, in the order 

 of superposition, are placed above 

 the wealden, and below the earliest 

 of the tertiary period, or eocene. 

 " In general, an interval seems to 

 have taken place between the com- 

 pletion of this formation, and the 

 deposition of those which repose 

 upon it; and the surface of the 

 chalk, at the line of junction, 

 usually bears marks of having 

 undergone, during that period, a 

 partial destruction subsequently to 

 its consolidation ; a bed of debris 

 being spread over it, consisting 

 chiefly of flints washed out of its 

 mass, and the surface being irregu- 

 larly worn into frequent cavities, 

 many of them of considerable depth, 

 filled with similar debris. On this 

 debris rests the plastic clay : here, 

 therefore, the transition from the 

 chalk to the more recent formations 

 appears to have been abrupt, not 

 gradual ; in a few instances, how- 

 ever, a bed of intermediate character, 



[ 82 ] C H A 



a cretaceous marie, is interposed at 

 the junction, which may seem to 

 countenance this idea, that where 

 the series of deposits was permitted, 

 from the circumstances under which 

 they have been formed, to proceed 

 quietly, such a gradation may have 

 taken place." fConyleare.j The 

 greatest thickness of the chalk strata 

 in England may be estimated at 

 from 600 to 1,000 feet. The organic 

 remains in the chalk formation are 

 exclusively marine. The nodules 

 and veins of flint which occur in 

 the chalk, show that water holding 

 silex in solution must have been 

 very abundant at the cretaceous 

 period, although we are ignorant 

 by what means silex may be dis- 

 solved in water. Mammalia are 

 not known in the cretaceous rocks. 

 The testacea hitherto obtained from 

 the various members of the cre- 

 taceous group amount to about one 

 thousand. The plants found in 

 the chalk of England and Prance 

 are principally marine. Sulphuret 

 of iron is the only metallic sub- 

 stance, or metalliferous ore, found 

 in either the upper or lower chalk. 

 The chalk hills of England are 

 bounded by a line which stretches 

 from south-west to north-east, and 

 they form three principal mountain 

 ranges. The first, leaving Berk- 

 shire, runs north through Bucks, 

 Bedfordshire, and Hertfordshire, to 

 Gogmagog hills, near Cambridge. 

 The second, passing from Berkshire 

 eastward, stretches through Surrey, 

 where it forms the Hog's Back, a 

 beautiful ridge extending from 

 Farnham to Guildford, and then 

 appears at Boxhill. This branch 

 forms the hilly country and the 

 Downs north of Reigate, Bletch- 

 ingly, and Godstone. It enters 

 Kent to the north of "Westerham, 

 and extends to Folkstone and Dover. 

 One division of this ridge is con- 

 tinued to the north coast of Kent, 

 and terminates at the North Fore- 



