on the Don and Tamar Rivers. 97 
The brown combustible schist exhibits at the elevation 
last mentioned a thickness of six to seven feet in one distinct 
seam, passing upwards into laminated clay rock of a yellowish 
colour, interstratified with thin layers of the schist. 
Below the six feet seam there is, for a space, the same 
alternation as above,—but uninterrupted beds of compact 
yellowish and bluish white clays succeed; and near the 
river's level there occur, in the clay pebbles of quartz, frag- 
ments of Pachydomi, and rounded pieces of the blue un- 
fossiliferous limestone of the Circular Pond Plains, which 
flanks the extreme Western Bluff, and afterwards crops out in 
great force along the course of the Mersey itself, far inland. 
Abounding in olefiant gas, as this combustible mineral of 
the Mersey does, it is scarcely possible to say whether it may 
be found available for any useful purpose: its peculiar and 
powerful odour would, to most persons, be a strong objection 
to its use as an ordinary domestic fuel ; and for the purpose 
of making illuminating gas it would have these disadvan- 
tages—it would not form a coke, and the earthy and slaty 
residuum would tend to choke up the retorts. The occurrence 
in considerable numbers of rounded pebbles of the compact 
blue limestone of the Circular Pond Plains and the upper 
portions of the Mersey in these sedimentary beds suggests 
the probability of this limestone existing now 7” situ at no 
great distance; and indicates a period when the relative 
height of land and water was such as to allow the ocean to 
lash and abrade its massive sides, and to deposit at its 
bottomthe smoothly worn fragments, intermingled with the 
various shells mentioned, in a matrix of clay with some sand. 
The occurrence of thick beds of fine clay and clay-schists 
without organic remains above the fossiliferous masses de- 
note a tranquil condition of superstant waters, compatible 
only with the character of a capacious and sheltered bay, or 
H 
