334 J. W. DAYIS ON A BONE-BED IN THE LOWER COAL-MEASURES. 



the land took place and was in course of time covered by a dense 

 vegetation, which ultimately formed the Better-bed coal. The roots 

 of the plants are found in the seat-earth below the coal, from which 

 the inference may be drawn that they grew and decayed where they 

 are now found, and were not washed from a distance. The land 

 became again submerged, probably forming an estuary, whilst the 

 materials forming the bone-bed were deposited on the coal. That it 

 was an estuary-deposit receives confirmation from several sources. 

 The fish-remains found imbedded in it belong to two distinct groups : 

 the Elasmobranchii, of which the sharks and rays are existing repre- 

 sentatives, are chiefly confined to salt waters ; whilst a second group, 

 the Ganoidei, have several living representatives which are only found 

 in fresh water, as the Lepidosteus, Amia, and Calamoichthys of the 

 rivers of America and Africa, whilst others, as the sturgeon, can live 

 either in salt or brackish water. It is by no means certain that the 

 habits of the fish during the Carboniferous period were exactly simi- 

 lar to those of their descendants ; but supposing that they were so, 

 it is not difficult to conceive, when the land was lowered sufficiently 

 for the formation of an estuarine deposit, that the detached teeth and 

 spines of the Elasmobranchs might be washed towards the shore by 

 the tides, and there mixed with the remains of Ganoids from the 

 river. This also appears probable when the broken and frag- 

 mentary condition of the fossils is considered ; for being constantly 

 subject to attrition by each succeeding wave, the state in which they 

 are found would be the natural result. 



After some time, the land was lowered still more, and the mud 

 brought down by the stream, being deposited in deeper water, 

 formed the bed of blue shale resting upon the bone-bed. The over- 

 lying strata of alternating beds of coal, shale, and sandstone lead to 

 the inference that the elevation and subsidence of the land occurred 

 repeatedly. 



Before proceeding to the enumeration of the fish- remains I have 

 been able to identify from the bone-bed, T wish to acknowledge my 

 indebtedness to the Earl of Enniskillen, Sir Philip de M. Grey Eger- 

 ton, and W. P. Sladen, Esq., who have kindly placed their collec- 

 tions at my disposal for comparison with my specimens, and also to 

 L. C. Miall, Esq., who identified the remains of Labyrinthodonts. 



ELASMOBKANCHS. 



1. Gyracanthtjs formostts, Agass. 



2. G. TUBERCULATUM , Ag. 



Pectoral and dorsal spines of this genus are frequently met with. 

 The bones of the pectoral arch are also found, and occasionally 

 patches of shagreen covered with small tubercles. 



The gyrating lines of G.formosus are sometimes found divided into 

 tubercles, which are characteristic of the second species, G. tubercu- 

 latum hut as the various intermediate stages can be traced in a 



