186 MR. BALD’S ALLUVIUM OF TWO ERAS IN SCOTLAND. 
90 feet deep*: it contains abundance of organic remains of trees, 
shells, &c., and is visibly forming every day: on the other hand, the 
old alluvial cover is of vast extent, occupying a large portion of the 
surface of Great Britain, is found at great heights and also under 
the level of the sea, and is of three kinds : first, sand; second, gravel; 
third, clay; the clay is sometimes mixed with sand, gravel, and 
boulder stones, which are several tons in weight. The whole is 
without horizontal divisions into beds or strata, and both large and 
small boulder stones are found mixed irregularly through every part 
of it. In some places it attains the thickness of 160 feet; besides 
boulder stones, it contains gravel (i. e. rounded fragments) of almost 
every kind of rocks, and angular fragments of the adjacent rocks, 
which are often of a softer nature than those which have been rolled 
to pebbles. It is this old alluvial cover in which the elephants’ 
tusks are found; but besides these and the bones found with them, it 
has been observed to contain no other kind of organic remains; the 
absence of such remains, and irregular manner in which the ma¬ 
terials of this deposit are mixed together, lead to a conclusion that 
they were collected by some violent and sudden convulsion totally 
different from the daily and gradual process by which the present 
alluvium has been and continues to be formed.” 
* It was in this alluvium, that the entire skeleton of a large whale, which is now in 
the College Museum, at Edinburgh, was found a few years since; it must have been 
drifted and stranded there, while this part of the estuary was under the process of filling 
up by the deposits of the present sea. The bones of whales have been found in a nearly 
similar position at Pentuan, in an ancient estuary that is now filled up on the coast of 
Cornwall. A description of the stream works at this place is given in Vol. IV. of the 
Geol. Trans, p. 404. 
