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hollow interiors of these shells were of frequent occurrence, 
being revealed constantly after new blastings, the shock 
loosening and displacing the interior masses. 
Another feature of these concretionary masses, which is very 
significant, is this: that in every case where the central masses 
were broken up, fossils of one or other of the forms mentioned 
were found in the centre, apparently forming a nucleus to the 
mass. Over and over again I tested this by getting the work- 
men to break up the spheroidal cores they had kept for me, and 
in every case, without a single exception, one or more Ammo- 
nites, or occasionally a pocket of Brachiopods or Lamellibranchs, 
mingled with pieces of wood, occupied the centre of the block. 
On each face of the cutting, as one walked along, the same fact 
was evidenced in scores of examples. When the Club visited 
the cutting, Dr Wrieut gave particular attention to this im- 
portant fact, and had several cores broken up for his inspection. 
One very characteristic specimen (exhibited) from the centre of 
such a core, contains several small Ammonites, scores of small 
splinters of wood, and a colony of Brachiopods, showing the 
internal structure of the test wherever it has been accidentally 
broken into. 
So far I have confined myself to a description of the observed 
facts. I now submit an explanation to account for the remark- 
able features of this bed of Calcareous Sandstone. It is this: 
That this bed was very rapidly deposited ; that it was deposited 
not far from a land surface; that the Ammonitide and other 
animals were entombedalive, or at anyrate justnewly killed; that 
the bed rapidly consolidated ; that the concretionary character of 
the masses of rock is due to the decomposition of the organic 
matter of the entombed animals, the products of decomposition 
so affecting the enveloping sand and lime, then in a pasty con- 
dition, as to lead to an eccentric disposition around the animal 
nucleus, and the consequent formation of the shell-like layers. * 
* Since this paper was read, my friend, Dr Sm1rHE, has reminded me of P 
a description by JUKES of somewhat similar concretionary masses ; and in the 
4th edition of JuKEs’ School Manual of Geology, published recently, p. 143, 
there is an allusion to similar occurrences. 
