FOSSIL ELEPHANT. 
59 
Britain ; is found at great heights, also under the level 
of the sea; and is of three kinds, viz. Ist, Sand; ^d. 
Gravel ; and, Sd, C\ay. The clay is of two kinds, viz. Isty 
fine plastic clay, such as is used by potters ; and, 2d, clay 
intimately mixed with sand, gravel, and boulder-stones ; 
which last are sometimes found several tons in weight. It 
is this last kind of cover which at present I particularly re- 
fer to. 
I have had very frequent opportunities of seeing this 
kind of cover laid open from the surface, to the rock on 
which it rests, and have found it in thickness from a few 
inches to 1 60 feet ; and have always remarked, that though 
it contained boulder-stones, and gravel of almost every kind 
of rock, and detached angular fragments of the adjoining 
rock-stratification, I never had observed a single instance 
of an organic remain of any kind in it. This cover is 
known in Agriculture by the name of Till, and is impervious 
to water. The soil which covers it is generally thin, and 
not naturally fertile ; of itself, it is indeed one of the most 
sterile subsoils which is known. The first plant which most 
frequently strikes root upon it, after exposure to the air, is 
the common thistle, Carduus arvensis. 
As the Union Canal, which is now making betwixt this city 
and Falkirk, passes for 28 miles through a country chiefiy 
composed of this kind of cover, I took the opportunity of 
noticing if any organic remains were found in it ; and I 
requested my friend, Mr Hugh Baikd, civil engineer, who 
directs the canal operations, to be particular in his inquiries 
if any such remains were found, and to give me notice. 
Having been frequently along the Canal with him for these 
last three years, I had an opportunity of investigating the 
excavations as they proceeded. No appearance of any ani- 
mal or vegetable remain, however, was found, until tlie 
i8th day of J uly last, when tlic workmen, who were cut- 
