A. B. WYNNE, ON FROG-BEDS IN THE ISLAND OF BOMBAY. 1 



On the occtirrence of peog-beds at a locality Idtherto concealed, hut 

 exposed noio hy reclamation worJcs in Bombay Island, December 

 1867 ; by A. ^. Wynne f. g. s., Geological Survey of India. 



Since the examination which furnished data for the report on the 

 geology of Bombay Island, extensive operations for the reclamation of 

 the foreshore of Back Bay have laid open a large space on the east flank 

 of Malabar Hill, exhibiting its structure from its foot for a considerable 

 distance upwards, and thus confirming the view already ofiered of the 

 arrangement of the rocks- 



The excavation, which is about 350 yards in length and 140 feet in 

 depth, is situated at Chaopattee (see page 47, Eeport Geology, Bombay 

 Island, Mem., Geol. Survey, India, Vol. V), near the north-west 

 corner of the Bay. Its place in the frontispiece of the report would be 

 behind the Cotton Factory, the smoke from which is so conspicuous, and 

 more distant by about a mile. 



The site, which was chosen chiefly from its vicinity to the shore to 

 be reclaimed, proved fortunate, as the soft band beneath the hill is locally 

 thick, and instead of encountering the hard basalt, blocks of which from 

 above were strewn over the slope, the ashy beds and associated shales 

 afibrded materials much more easily extracted and well calculated for 

 forming the embankment when faced with blocks of the basalt. This 

 good fortune, however, appears to have been unforeseen. The base of the 

 hill was covered with detritus. Its true structure was not generally 

 known, and if the then recorded observations had been relied upon, only 

 a thin band of shales extending horizontally beneath the hill would have 

 been expected to occur. 



The soft band so well seen in this excavation consists of muddy and 

 ashy rock with intercalated layers of shale. Of these the lowest are hard 

 dark gray or bluish argillaceous rocks with thin black shaly partings 

 occurring as a band, of some two to three feet in thickness. The surface 



Memo. Geological Survey of India, Vol. VI, Art, 7. 



{ 385 ) 



