HARDWICKE'S SCIENCE-GOSSIP. 



179 



increasing the interest already attached to the 

 beautiful study of botany, and adding yet deeper 

 feelings of reverence towards the great Creator. 



THE CRAB A GEOLOGIST. 



THE following notice of a natural phenomenon 

 which I witnessed may be of interest to 

 readers of Science-Gossip :— 



As I was walking with a friend, some ten years 

 ago, along the sandy shore of the Tenasseriin coast, 

 I was surprised to see in one place a large number 

 of apparently rolled pebbles or stones extending 

 along the beach for some distance, just above high- 

 water mark. The reason for my surprise was that 

 such a thing as a pebbly beach is nowhere met with 

 (at far as my experience goes) on this coast. The 

 entire coast-line of Tenasserim, from Amherst on the 

 north to the Packchanriver on.the south, consists 

 of alternating'bold granite bluffs, which jut out into 

 the sea, and semicircular sandy bays, with here and 

 there an extensive mud-flat and mangrove swamp 

 at the mouths of creeks and rivers. It is very hard 

 to find a stone anywhere on any of the sandy 

 beaches. Granite iDOulders of various sizes are 

 frequently met with on the sand, but that is all. 

 The very unusual appearance, therefore, of a num- 

 ber of stones, resembling shingle, collected together 

 in one place, surprised me. 



After my companion and I had amused ourselves 

 with throwing about some of these stones, which 

 were so hard as to have required a hammer to break 

 them, we found that others (those nearest to the 

 sea) were soft— of a firm cheesy consistency — so 

 that the end of a walking-stick could be forced into 

 or through [them. This naturally increased our 

 surprise ; we therefore set ourselves to discover, if 

 possible, the cause of this strange phenomenon. We 

 werevnot long in doing this. The actual process of 

 manufacture was witnessed. It may be stated here 

 that the part of the coast spoken of is not far from 

 the mouth of the Tavoy river, which expands into a 

 broad estuary several miles across. This river 

 carries down towards the sea a vast quantity of 

 mud, the greater part of which is distributed along 

 the coast-bottom to the south, owing to the direc- 

 tion of the river, which flows from north to south, 

 the run of the coast-line being the same. At 

 Mergui, also, only sixty miles to the south, another 

 arge river, the Tenasserim, pours down its quota of 

 mud, and this also is coniined near the coast by the 

 islands of the Mergui Archipelago, which stretch 

 from near the mouth of the Tavoy river on the 

 north, to near Junk-Selung on the south. I have 

 dredged the bottom at intervals between Tavoy and 

 Mergui, and found it to be mud the whole way 

 inside the islands. 



The consequence of this 'is, that although some of 



the reaches of sand on this part of the coast are 

 very fine, the sand is, nevertheless, comparatively 

 shallow, and it fines off rapidly to seaward, until, a 

 little way out, pure mud is reached. In some parts, 

 at low water, a very thin layer of sand covers the 

 mud below. This mud is exceedingly stifi", and of 

 the colour of the well-known blue lias. To come 

 now to the manufacture of these stones. The 

 crabs, which abound on tropical seashores, were here, 

 although too small to be worth catching for the pot, 

 considerably larger than I had seen in similar situa- 

 tions elsewhere ; and, as the tide was low, we saw 

 numbers of them running about the wet sands, and, 

 as we approached them, they would dive rapidly 

 down into the small round holes which it is their 

 habit to burrow for themselves. In making these 

 holes the crabs (as is, no doubt, known to many) 

 throw out the soil in small round pellets or 

 balls. I had frequently noticed at Amherst the 

 tiny round balls of sand strewed about the holes 

 which the smaller crabs there make. When the 

 ejected material is sand,'. these balls are, of course, at 

 once dissolved at return of each tide. But here, as 

 the sand was only in a superficial layer, and the 

 crabs were larger, in making their holes they pene- ■ 

 trated through the sand and reached the mud ; con- 

 sequently the material thrown up was stiff clay, and 

 the balls were larger in proportion to the size of 

 the workers. Looking at these balls of clay as the 

 tide was turning to flood, we soon perceived how 

 our stones were made. The ripple of an advancing 

 wave would first roll two of the smaller balls into 

 one, then another wave would do the same^with 

 two larger ones, until, by a repetition of this very 

 simple process, rounded balls of various sizes were 

 formed, and ultimately, as the tide advanced, flung 

 up high and dry upon the sand, out of the farther 

 reach of the waves. Here they lay and hardened, 

 until, in form, in weight, and in general appearance, 

 they resembled bond-fide water-worn fragments of 

 blue lias. There was a long line of these stones 

 on the sand just above high-water mark, and they 

 must have been numbered by thousands. 



And, now, to offer a remark or two on this sub- 

 ject. It is easy to imagine that these stones, so 

 strangely originated, may, at some distant day, be 

 imbedded in a stratum of sandstone, and may, per- 

 adventure, form the subject of investigation by some 

 future geologist (supposing, that is, the race o 

 geologists to bel as enduring as the strata which 

 they make their study), and if so, they would pro- 

 bably be pronounced to be genuine waterworu frag- 

 ments of rock older than the sandstone in which 

 they were found imbedded. In this instance, our 

 imaginary geologist will have been mistaken ; for 

 though indeed formed partly by the action of water 

 on a seashore, they were so formed by a constructive, 

 and not a destructive, process ; and, moreover, they 

 would be of exactly the same age as the sandstone. 



