256 Proceedings of the Royal Physical Society. 
burrows of the much more perishable annelids and other soft-bodied animals. 
The question suggests itself as to whether calcareous lamellibranchs had as 
yet adapted themselves to such a life by producing structures that would 
allow of the habit. The only examples I have observed of the casts of 
lamellibranchs in sandstone have been detached valves of such flattened 
forms as Aviculopectens, and these were lying along the bedding planes in 
such a manner as to show plainly that they had been carried there after 
death. This evidence, though negative, is in accordance with the fact that 
no pallial sinus has been observed in a Carboniferous lamellibranch. 
EXPANSION IN CALCAREOUS SEDIMENTS. 
In working over sections of the Carboniferous as well as other formations 
where calcareous rocks alternate with shales or sandstones, one can hardly 
fail to see that the calcareous bands are more or less folded independently 
of the adjacent layers. Often, as is well displayed in the old railway cutting 
at South Queensferry, the calcareous beds associated with dark sandy shales 
are overfolded and even overthrust upon themselves at almost regular short 
intervals, and often staved together and brecciated without a corresponding 
disturbance being visible in the shales. The limestone beds exposed on the 
shore at Skateraw and Long Craigs, south of Dunbar, are thrown into 
innumerable small domes and basins. In the successive beds of the Hosies 
Limestones, which form strips parallel with the coast-line on the wave- 
eroded shore to the south of Seafield Tower near Kirkcaldy, each band of 
limestone in turn is seen to be traversed at regular intervals of about 20 
yards or so by very oblique upthrust faults showing displacements of several 
feet, sometimes in one direction and sometimes in the opposite one, but none - 
of these thrust planes go far up or down into the adjacent strata. One 
cannot but see that in all the cases these beds have been subjected to lateral 
thrust after consolidation. It is also plain that the force which produced 
the tangential thrusting must have developed within the limestones them- 
selves. The study of calcareous strata almost everywhere shows that lime- 
stones and clay ironstones set or become solid at or near the surface of 
accumulation. Most of these limestones are of organic origin, and aragonite, 
the densest and heaviest form of calcium carbonate, enters very largely into 
the skeletons of calcareous organisms, During the process of setting, aragonite, 
which is markedly unstable, in changing into the stable but more bulky 
calcite, may have supplied the necessary tangential pressure. In many cases, 
in every formation studied by me from the Cambrian limestones up to the 
Carboniferous Limestone, breccias of the broken-up layers of limestone have 
heen observed where limestone of the same type as the brecciated fragments 
