CHAP. X.] 
THE EARTH’S AGE. 
211 
Limestone full of characteristic fossils, at a depth of only 800 
feet. Here we have an enormous gap, showing that none of 
earlier Secondary or late Palaeozoic formations extend to this 
part of England, unless indeed they had been all once elevated 
and entirely swept away by denudation. 1 
But if we consider how such deposits are now forming, we 
shall find that the thinning out of the beds of each formation, 
and their restriction to irregular bands and patches, is exactly 
what we should expect. The enormous quantity of sediment 
continually poured into the sea by rivers, gradually subsides to 
the bottom as soon as the motion of the water is checked. All 
the heavier material must be deposited near the shore or in 
those areas over which it is first spread by the tides or currents 
of the ocean ; while only the very fine mud and clay is carried 
out to considerable distances. Thus all stratified deposits w r ill 
form most quickly near the shores, and will thin out rapidly at 
greater distances, little or none being formed in the depths of 
the great oceans. This important fact was demonstrated by 
the specimens of sea-bottom examined during the voyage of 
the Challenger, all the “ shore deposits ” being usually confined 
within a distance of 100 or 150 miles from the coast, while the 
< ' deep-sea deposits ” are either purely organic, being formed of 
the calcareous or siliceous skeletons of globigerinte, radiolarians, 
and diatomacese, or are clays formed of undissolved portions of 
1 The following statement of the depths at which the Palaeozoic forma- 
tions have been reached in various localities in and round London was 
given by Mr. H. B. Woodward in his address to the Norwich Geological 
Society in 1879 : — 
Deep Wells through the Tertiary and Cretaceous Formations. 
Harwich at 1,022 feet reached Carboniferous Rock. 
Kentish Town „ 1,114 „ „ Old Red Sandstone. 
Tottenham Court Road ,, 1,064 ,, ,, Devonian. 
Blackwall „ 1,004 „ „ Devonian or Old Red Sandstone. 
Ware „ 800 ,, „ Silurian (Wenlock Shale). 
We thus find that over a wide area, extending from London to Ware and 
Harwich, the whole of the formations from the Oolite to the Permian are 
wanting, the Cretaceous resting on the Carboniferous or older Palasozoic 
rocks ; and the same deficiency extends across to Belgium, where the 
Tertiary beds are found resting on Carboniferous at a depth of less- than 
400 feet. 
