186 NATURAL HISTORY. 



excavations hitherto made on the Flats have not yet passed the level 

 at which they attained this circumference, and the length represents 

 the extreme diameter of a clod ordinarily loosened by a stroke of the 

 pick in the work of excavation. When this is lifted, of course so 

 much of the tube as it contains is snapped off and carried away with 

 it. I daresay if we were to dig carefully downwards from the 

 present level of the Flats, we should be able to uncover specimens of 

 greater length gradually increasing in circumference, till at last we 

 reached the lower or big end, as to which I shall have something to 

 say presently, but a specimen of which I have not yet succeeded in 

 finding. 



One curious characteristic of these tubes is the way in which they 

 change their direction, as shown in the group of specimens marked 

 No. 4. I would particularly draw your attention to a feature in these 

 to which I shall have occasion to refer again, viz., that wherever 

 one of these changes in direction occurs, it is marked by a little 

 rounded knob or excrescence on the shell. Probably these changes 

 in direction were necessitated, either by the inhabitant of the shell 

 coming on some hard substance through which he could not bore, or 

 by his being obliged to work in a very confined space, by reason of 

 his neighbours crowding on him, or by reason of the limited extent of 

 the soil suitable for his operations at the scene of his labours. The 

 excrescences, I presume, were formed by the animal closing the end of 

 his tube in the old direction when he started in the new to pre- 

 vent the entry in his rear of water or mad or animals which might 

 cut off his connection with his upper or smaller end. 



What then are these tubes? Before attempting a solution of 

 that question, it may be as well to state what they most certainly are 

 not. They are not calcareous casts of the stems and roots of aquatic 

 plants, formed by the deposit of lime held in suspension by the water 

 in which they grew on vegetable substances which have since decayed, 

 leaving only their mineral envelopes. You may think that in 

 enunciating such a theory for the mere purpose of demolishing it I am 

 but setting up a mau of straw for the pleasure of knocking him 

 down. But I remember Major Frere once telling me of a passage in 

 some work on the geology of Bombay, in which it was suggested that 

 the shelly tubes found on the Byculla Flats were casts of the roots of 

 the mangrove bushes once growing there when the place was a muddy 

 salt marsh. I have forgotten the name of the book, and I have not 

 been able to find it since ; but I believe it came from the library of the 



