^ J. L. LOBLEY — CRETACEOUS ROCKS OF ENGLAND. 



have taken place, that a rock maybe wanting though those usualh' 

 found next below and above it are present. The geological scale, 

 however, tells us without doubt the order of superposition of those 

 rocks which we may find at any place. Thus we may certainly 

 predicate the absence at any locality of the rocks which the scale 

 indicates to be above those there exposed. 



The whole of the sedimentary rocks, or those formed by the 

 consolidation of sediment at the bottom of water, are di^-ided, in 

 accordance with their relative age, into three great groups, com- 

 monly called Primary, Secondary, and Tertiary, or, as they are 

 now more philosophically named, Palaeozoic, Mesozoic, and 

 Cainozoic ; but in this lecture scientific words will be used 

 sparingly. The Cretaceous rocks are the uppermost and the 

 newest of the second of the three great divisions (see Fig. 1), and 

 hence it will be at once seen that enormous thicknesses of rocks 

 had been deposited, and vast periods of time had elapsed, before the 

 Chalk was formed : and when it is remembered that the Chalk 

 itself has been found to have a maximum thickness of 1000 feet, 

 and to consist of material extracted by microscopic animals from 

 clear sea-water, the vastness of the period during which the rocks 

 have been in coui'se of formation must be forcibly impressed upon 

 the mind. 



As will be seen from the accompanying map (Fig. 2), the Creta- 

 ceous rocks of England extend in a roughly fan-shaped or diverging 

 manner from the coast of Dorsetshire to the north-east of the 

 county of Norfolk, with a further extension forming the "Wolds 

 of Yorkshire and terminating at Flamborough Head. "West of 

 "Weymouth there are merely a few detached outlying beds of 

 Cretaceous age, the remnants of deposits the greater portion of 

 which have been removed by Nature's destroying forces. 



The Chalk forms by far the most conspicuous member of the 

 Cretaceous groiip as exhibited in England, and the geogi-aphical 

 extension of the Chalk coincides generally with the extension of 

 the Cretaceous rocks considered as a whole, the other members of 

 the system fringing or lying within those gr(>at lines, and for the 

 most part roll-like extensions of Chulk called Downs and "Wolds, 

 which form so marked a feature of the physiography of the southern 

 and eastern parts of our island. 



Three great ribs, as it were, of Chalk can be clearly traced. One, 

 the southernmost, extending along the coast, forms the coast hills 

 of Dorsetshire, the ridge of high land running through the Isle of 

 "Wight from the " Needles " to Culver Clifi', and further still to the 

 east, the well-known South Downs terminating in Beechy Head. 

 The second branches from the one just described in Hampshire, 

 and though also running east, extends along the northera side of 

 tlie "Weald of Surrey, Sussex, and Kent, and so forms the North 

 Do\vns, which, like the South Downs, terminate only when the 

 sea is reached. The cliflPs from Margate to Kamsgate, and those 

 liold headlands, Dover Cliffs, are the extremities of tlie second rib. 

 The third great line of Chalk gives to England Salisbury Plain, the 



