CHAPTER I.
GENERAL DESCRIPTION OF SALSETTE.
Tbe island of Sashthi, or Salsette, lies just north of the 19th parallel of
North Latitude on the west coast of India, and close to the mainland. The
táluka of Salsette in the Thana District, to which it belongs, and of which it
forms all but a strip on the mainland of about 47 square miles, known as the
Khairan Patti, is some 250 square miles in extent, Salsette island is separated
on the North and East from the mainland by a creek, of which the northern
arm is known as the Bassein Creek, and the eastern the Thána Creek. To the
South lie Bombay Island and Bombay Harbour. The taluka has a population
of some 150,000 people in 140 towns and villages.
PHYSICAL GEOGRAPHY AND GEOLOGY.—The most striking
feature of the geography of Salsette island, and one which has a very important
bearing on its malariology, is its range of hills, the highest peaks of which are
over 1,500 feet, though within a few miles of the sea, This range forms, as it
were, the backbone of the island, and runs, diminishing in height, from the
northern end southward. In the southern portion of the island is an area devoid
of hills, though in the south-east corner, in what is known as the Island of
Trombay, at the head of Bombay harbour, there is a hill 1,000 feet in height,
of the same nature as the hills that run down the centre of the island.
Spurs from this main line of hills run westwards towards the sea.
Among the hills lie two artificial lakes, Tulsi and Vehar, which provide
part of Bombay's water-supply. A third, Powai Lake, has in more recent
times been constructed for the same purpose south of Vehar, though the shallow-
ness of the bed has prevented the water stored from being of a quality that
could be used,
The west coast is deeply indented by creeks, the two principal of
which are the Malád and Manori Creeks, which detach, or almost completely
detach, considerable portions of the land at spring tides.
It is unfortunate that there has never been a geological survey of
Salsette. A geological map would have been useful in the present connection,
for, as will be seen, there is a relation between the geology of the island and its
malariology.
The hills of Salsette are of the same volcanic origin as those of the
rest of the Konkan and the Deccan at this latitude. The relative steepness of
its hills on their eastern face is as noticeable as in the case of the hills of
Bombay Island, and depends on the fact that there is a dip in the strata to the
westward of from 10° to 15°, the strata near the coast being, as a matter of
fact, of a higher series than those far up in the ghauts. Most of this volcanic
rock in Salsette is trap, derived from the lava of ancient volcanos, but in places
the rock is breccia, derived from their ash.
There is certain amount of sedimentary rock to be found, however,
especially in the South of the island, where it is continuous with that lying in
the bed of what was once a great fresh-water lake, part of which covered areas
now in the Island of Bombay.
The soil derived from the disintegration of the trap, which, if it contain-
ed more organic matter and were of a darker colour, would be known as a
cotton soil, extends from the bases of the hill scarps clown towards the sea. By
the sides of the creeks it gives place to alluvium, which, brought down to the
coast by streams, has been washed back by the sea to form the flats that line
the creeks of the island and are mostly submerged at spring tides. The alluvium
is thus heavily impregnated with salt.