104 Mr Geikie on a Rise of 
pipes, probably marking the remains of the stems of plants.* 
This stratum passes up into a bed (5), about six feet thick, of 
dark silt or sandy clay well stratified, having thin lenticular 
interlaminations of sand, with occasional oyster-valves, a few 
stones, and fragments of bones and pottery. The upper part 
of this bed becomes more sandy, and graduates into the super- 
incumbent stratum of brown sand (6). The highest bed of 
the section (7) consists of stratified sand and shingle full of 
littoral shells, and some of the stones having balani still 
attached. The irregular deposit (marked h in the diagram), 
which rests unconformably upon the edges of the strata just 
described, is a mass of loose humus, which has been thrown 
down here at no distant date, perhaps to fill up an irregularity 
of the surface. It is full of stones, bricks, bones, pieces of 
earthenware, tobacco-pipes, &c., and its origin is sufficiently 
explained by a large board a few yards distant—“ Rubbish 
may be laid down here free.” 
It is with the stratum marked 5 that we have chiefly to 
deal. But before entering into its details, I would dwell 
pointedly on the fact that it is a regularly stratified deposit, 
with thin parallel interlaminations of sand and clay; its 
oyster-valves and stones lie horizontally, and it passes upward 
by gradations into brown sand, which is covered by well 
stratified shell-sand and gravel. It cannot for a moment’ be 
confounded with the dark earth h, in which no trace of strati- 
fication can be detected, and which, moreover, rests on the 
edges of the other deposits. Whatever may be the contents 
of this bed of silt, they are undoubtedly of contemporaneous 
deposition ; in other words, all the materials imbedded in the 
stratum were laid down at the same time with the stratum 
itself. And that this deposition and arrangement were effected 
* JT have seen similar pipes produced in the clay below a peat bog, by the 
decomposition of the salts of iron round the roots of plants, the bark becoming 
crusted with the oxide, and eventually replaced by it, while the internal woody 
matter has disappeared, leaving only a set of branching pipes to represent the 
roots and rootlets. When I first saw the pipes in the sand-pit at Leith, they 
appeared to me to resemble annelide burrows; but a more careful search 
showed that they not unfrequently branched, and that they could hardly be of 
other than vegetable origin. They may have arisen when the stream flowed 
over the clay, on which a scrubby and semi-aquatic vegetation grew. 
