670 Physiography. [ October, 
watch any little rill which falls into a pool on the sea-shore, we 
shall soon find out. We shall see that the sand and other material 
which it carries are built up into a little delta, while some of the 
finest material is spread at large over the bottom of the pool. 
Large rivers carry vast quantities of mud and sand and silt (much 
of which is washed off the land by the rain) to the sea. Experi- 
ments of mine on the Thames, at Surbiton, show that in fine 
weather, when the river was low and fairly clear, solid matter in 
suspension was being carried seawards at the rate of 9767 tons per 
annum ; while, when the river.was in extreme flood, matter at the 
rate of 524,940 tons per annum was passing in this way down to- 
wards the sea. With the great rivers of the world of course the 
amounts are still more enormous. Sir Charles Lyell calculated 
“that if a fleet of more than eighty Indiamen, each freighted with 
about 1,400 tons weight of mud, were to sail down the Ganges 
every hour of every day and night for four months continuously, 
they would only transport from the higher country to the sea a 
mass of solid matter equal to that borne down by the Ganges in 
the four months of flood season.” All the matter carried down 
in this way is built up, layer upon layer, into a vast delta deposit, 
or strewn over the bed of the ocean. Of such layers much of the 
crust of the earth, the sand and clay at the top of the cliff behind 
us for example, is composed. 
But besides the matter carried down by rivers in suspension, a 
vast amount is carried down in solution. Take the Thames for 
example. For every grain transported mechanically, more than 
twenty grains are carried down chemically. Every gallon con- 
tains some twenty grains of lime salts, and about two grains of 
common table salt, or chloride of sodium. These also are carried 
out into the sea, in which the chloride of sodium, along with cer- 
tain other salts, accumulates on the evaporation of the water, and 
thus forms the brine of the ocean, while the carbonate of calcium 
is separated by living creatures and built up into some sort of 
pure limestone. Of such limestones also much of the crust of 
_ the earth, the chalk of the cliff behind us for example, is com- 
| Rose: 
We have thus seen what the streamlet is doing. It is aiding 
: the rivers of the world to carve out valleys, and it is carrying sea- 
vards- the fine mud and sand which result from its own work an 
that of min, to Sn ie to abe pamework ofa future continent. 
