PART 3.] 
Blanford: Geology of Bombay Presidency. 
101 
Patan, which are now only reached by high floods; and dead oysters, evidently quite recent, 
were found in various creeks and especially in one at Porbandar, 20 feet above the level at 
which they now live. The evidence collected by Mr. Theobald appeared to show that a rise of 
10 feet had taken place in the course of the year 1856. The changes of level in the Ban of 
Kachh during the earthquake of 1819 are well known, but in that instance, elevation of one 
tract was accompanied by depression in another. The vast expanse of water which Sir 
A. Burnes found around Sindri in 1828 has, however, now been mainly reconverted into dry 
land; and Mr. Wynne in 1868 reached the ruins of Sindri fort from Kachh on a camel. 
This change appears due to the deposition of silt, the cause to which may be attributed 
the conversion of the whole Ban into a land area. 
Alluvium, besides occupying the delta of the Indus, the Ean of Kachh, the southern 
coast of the same province, and a large tract extending northward and eastward from the Gulf 
of Khambayat, covers nearly the whole of Surat district, and occupies a considerable proportion 
of the country to the southward, forming plains which, near the coast, intervene between the 
trap bills as far south as Bombay. It appears probable that some of the hills in the Northern 
Konkan have been promontories or even islands in the sea, and it is recorded that within his¬ 
torical times the hills of Bombay island were unconnected with each other. Their union has 
been due partly to artificial means, but chiefly to the accumulation of sand and silt. Unques¬ 
tionably, unless man interfere, or some great change take place in the configuration of the 
country, the harbour of Bombay, the sole survivor of the inlets, which must once have been 
numerous, must be gradually silted up in the course of age. But as no stream of importance 
enters the harbour, the process is not likely to be so rapid as to cause serious concern as yet 
to those interested in the commerce of the port. 
Littoral concrete .—An agglutinated calcareous mass of shells and gravel is found in 
many places along the coast. Some is seen in Bombay island, the esplanade consisting of 
it, and a part of the fort being built upon it; it also occurs at Mahim aud in places on the 
shores of the harbour. To the northward it is met with here and there as far as Daman; 
it may show slight elevation of the coast line, but the amount of rise is vory trifling. 
Upon the milliolite of Kattiawar the same formation is much more largely developed. 
It here assumes the appearance of a calcareous grit, containing marine shells and corals, and 
occasionally attaining a thickness of 60 feet. The species of animals iound in it are, so far 
as is known, identical with those now inhabiting the coast. The evidence thus afforded of a 
recent elevation is an addition to that previously quoted. 
Blade soil .—Soils scarcely enter into the geology of a country, as they are simply the 
surface altered by exposure, organic agency and agriculture, but it is impossible entirely 
to overlook the widely spread “ rigar” or “ cotton soil. ” This is a black, grey or brown 
loam, varying much in character; tenacious and adhesive when wetted; light, crumbling 
and intersected by cracks when dry. It is found throughout the trap area, being in this 
instance a product of the decomposition of the volcanic rock, and every step in the passage 
from one to the other may often be witnessed in small roadside sections. It does not, 
however, follow that all soils derived from the trap are black, nor that no black soil is 
produced by the decomposition of other rocks. Bed soil is often seen within the trap area; 
and true cotton soil, inferior in fertility, however, to that produced by the volcanic formations, 
is met with in Southern India, in the Kaveri valley for instance, in a country which there 
is no reason to suppose ever contained trap. A very similar black alluvial deposit forms 
in the back-waters of the coast. 
“Eigar,” in short, appears to be a more or less argillaceous soil, impregnated with 
organic matter. 
