PREHISTORIC BOMBAY. 147 



consist in part of estuarine clay, and in part of marine sand. The 

 former must have been deposited when Bombay was a group of islands 

 separated by tidal creeks, such as we see to this day in abundance 

 about JSalsette and the coast of the Concan. It contains numerous 

 roots of mangrove bushes bored by a species of teredo, showing that 

 the soil in which they grew was a muddy salt marsh half way be- 

 tween high and low water marks. The marine sand, in places 

 caked together into compact masses, to which the name has been 

 given of " littoral concrete," consists almost wholly of sea shells that 

 lived below low water mark. But, where both are found together, 

 the low tide sand is fomid above the half tide clay, and in this order 

 both are found together in places above high water mark. 



But this is not all. At a spot in Byculla, 20 feet above the level 

 of the sea, has been found below the clay that underlies the littoral 

 concrete, a band of brown earth, evidently a salt water deposit, for 

 it contains nodules of lime enclosing shells of the thin oyster, which 

 from its position must be older than the blue clay, but from its 

 appearance must have been exposed to atmospheric weathering. 



Here, then, is another strange fact recorded in our book. After 

 the volcanoes had so piled hills as we have seen on the fresh water 

 swamp on the main-land, and these had by a subsidence of the coast 

 been broken off the main-land and cast into the sea as islands, and 

 had there lain undisturbed long enough to allow the deposit of the 

 silt which forms this band of brown earth, there came an upheaval 

 of the land that raised the floor of the sea above high water mark 

 and exposed it to the action of the weather. This was followed by ' 

 another subsidence that brought the band of brown earth below the 

 level of half tide mark long enough to allow the deposit on it of 

 the mud of tidal creeks and the growth of mangrove forests. Then 

 again the land sank down, till what had been salt marsh became deep 

 sea, and on the estuarine clay was deposited the shelly sand of the 

 littoral concrete. Then another change, this time an w/>-heaval, and 

 lo ! brown earth, blue clay, and littoral concrete, are together pushed 

 up above the level of the highest tide ! 



This change in the level of the Flats, for a reason I shall presently 

 point out, probably pushed them up considerably higher than they 

 now are, and possibly connected all the rocky islets in one. If so, 



