Ch. XXIII.] FORMER CONTINENTS WHERE NOW SEA. 
329 
respecting the different circumstances under which we conceive 
the secondary and tertiary strata to have originated. We have 
there hinted, that the former may have been accumulated in an 
ocean like the Pacific, where coralline and shelly limestone are 
forming, or in a basin like the bed of the western Atlantic, 
which may have received for ages the turbid waters of great 
rivers, such as the Amazon, and Orinoco, each draining a con- 
siderable extent of continent. The tertiary deposits, on the 
other hand, may have been accumulated during the growth 
of a continent, by the successive emergence of new lands, and 
the uniting together of islands. During such changes, inland 
seas and lakes would be caused, and afterwards filled up with 
sediment, and then raised above the level of the waters. 
That the greater part of the space now occupied by the 
European continent was sea when some of the secondary rocks 
were produced, must be inferred from the wide areas over 
which several of the marine groups are diffused ; but we do 
not suppose that the quantity of land was less in those remote 
ages, but merely that its position was very different. In the 
above tabular view of the secondary rocks, we have shown 
that immediately below the division No. 1, or ' the chalk and 
green-sand,' is placed a fresh- water formation called, in the 
south-east of England, the Wealden. This group has been 
ascertained to extend from west to east (from Lulworth Cove 
to the boundary of the Lower Boulonnois) about 200 English 
miles, and from north-west to south-east (from Whitchurch to 
Beauvais), about 220 miles, the depth or total thickness of the 
beds, where greatest, being about 2000 feet *. 
Now these phenomena most clearly indicate, that there was 
a constant supply in this region, for a long period, of a consider- 
able body of fresh water, such as might be supposed to have 
drained a continent, or a large island, containing within it a lofty 
chain of mountains. Dr. Fitton, in speaking of these appear- 
ances, recalls to our recollection that the delta of the newly-dis- 
covered Quorra, or Niger, in Africa, stretches into the interior 
* Fitton's Geology of Hastings, p. 58, 
