HUGHES : INGLEBOROUGH. 
261 
When we remember that this great mass of pure limestone 
is made up of the crushed fragments of shells and other cal- 
careous parts of animals, it seems at first difficult to explain 
why we find so few whole specimens throughout great thick- 
nesses of rock, whereas where such occur here and there they 
are remarkably well preserved. The analogy of the chalk, 
which is an earthy limestone similarly composed of comminuted 
calcareous parts of organisms, with well preserved specimens 
occurring here and there in bands or sporadically, teaches us 
that this character does not depend upon exceptional causes, 
but has to do with the ordinary mode of accumulation of great 
masses of limestone, without the intermixture of other sediment. 
These limestones were formed in dear water, but, as we are 
assured that the fauna does not in either case indicate deep 
water, we may infer that it was a sinking sea bottom teeming 
with life. 
But why were the hard parts of the molluscs, the crustaceans, 
the echinoderms, all broken up into sand and mud ? If we 
turn to recent seas where corals abound, we find vast masses of 
coral which have been broken up by the lash of the waves and 
formed into great terraces and sloping banks of debris on Avhich 
other corals build.* 
In some parts of the world now, and in many successive 
geological formations in the past, we find remains of fish fur- 
nished with strong palatal teeth, with which they scrunch up 
the shells of the animals on which they feed. The fragments 
are rejected and strewn over the floor of the sea and, where 
further broken and rolled by the action of the waves, form a 
calcareous sand and mud. Some shells and echini secreted 
among the recesses of branching corals are saved, and an empty 
shell would not be touched by animals seeking food. Such 
accidents would account for much of what we see in the Car- 
boniferous and Cretaceous Limestones. 
The greater part, however, of recent limestones and probably 
of those of ancient times, is due to the same causes as produce 
the vast deposits of mud, sand, and shingle, of which the rocks 
See Murray, Voyage of the Challenger. 
