176 
ELEMENTS OF GEOLOGY. 
submergence have been lost; but a few patches of estuarine 
and fresh-water formations escaped denudation by submer¬ 
gence. To these belong the peaty clay from which several 
mammoths’ tusks and horns of reindeer were obtained at Kil- 
maurs, in Ayrshire, as long ago as 1816. Mr. Bryce in 1865 
ascertained that the fresh-water formation containing these 
fossils rests on carboniferous sandstone, and is covered, first 
by a bed of marine sand with arctic shells, and then with a 
great mass of till with glaciated boulders.* Still more re¬ 
cent explorations in the neighborhood of Kilmaurs have 
shown that the fresh-water formation contains the seed of 
the pond-weed Potamogeton and the aquatic Ranunculus; 
and Mr. Young of the Glasgow Museum washed the mud ad¬ 
hering to the reindeer horns of Kilmaurs and that which fill¬ 
ed the cracks of the associated elephants’ tusks, and detect¬ 
ed in these fossils (which had been in the Glasgow Museum 
for half a century) abundance of the same seeds. 
All doubts, therefore, as to the true position of the remains 
of the mammoth, a fossil so rare in Scotland, have been set 
at rest, and it serves to prove that part of the ancient conti¬ 
nent sank beneath the sea at a period of great cold, as the 
shells of the overlying sand attest. The incumbent till or 
boulder clay is about 40 feet thick, but it often attains much 
greater thickness in the same part of Scotland. 
Fig. 107. Fig. 108. 
Astarte borealis, Chem.; {A. Leda lanceolata {ob- 
arctica, Moll.; A. com- longa), Sow. 
pressa, Mont.) 
Fig. 109. 
Saxicava rugosa^ 
Penn. 
Fig. 110. 
Pecten islandicus, 
Moll. 
Fig. 111. 
Natica clausa, 
Bred. 
Fig. 112. 
Troplion clathra- 
tum, Linne. 
Northern shells common in the drift of the Clyde, in Scotland. 
Marine Shells of Scotch Prift .—The greatest height to 
which marine shells have yet been traced in this boulder 
* Bryce, Quart. Geol. Journ., vol. xxi., p. 217. 1865. 
