8 Coal- Formation Fossils. 



ear-bones, as in the Crag, and of small vertebrae. No ceta- 

 ceans were met with, no relics of terrestrial mammals, 

 although at some points they approached near to the shore 

 so as to dredge up a few fragments of wood. In two or three 

 instances only were any articles of human manufacture, 

 such as a glass bottle, fished up. If reliance could be placed 

 on negative evidence, we might deduce from such facts, that 

 no cetacea existed in the sea, and no reptiles, birds, or quad- 

 rupeds on the neighbouring land. 



Coal- Formation Fossils. 



One solitary helix, which had been carried out to sea by 

 a hermit crab, was brought up from a depth of six fathoms ; 

 but no freshwater mollusca were obtained, probably because 

 their shells are in general very fragile. 



The absence even in the coal-measures of land- shells is a 

 singular and, if I mistake not, significant fact. The known 

 living species of the genera Helix, Cyclostoma, Bulimus, 

 Achatina, Pupa, and Clausilia exceed 2000 in number ; and 

 not one of these genera, nor any of the pulmoniferous mol- 

 lusca, such as Lymneus, Planorbis, Physa, &c., have as yet 

 been detected in any one of the primary strata from the 

 Silurian to the Permian inclusive. Yet no one who reflects 

 on the great number of palaeozoic marine shells, and the 

 extent to which they can be arranged under the genera or 

 families established for the classification of recent testacea, 

 can reasonably doubt that the lands of those periods were 

 also inhabited by mollusca. 



Some few shells of the coal-measures have been referred 

 to the genus Unio, and others to an annelid allied to Spi- 

 rorbis, and called Microconchus, probably an inhabitant of 

 brackish water. That other land and freshwater shells 

 should be so rare as hitherto to have escaped detection sur- 

 prises me the less when I remember how diligently I searched 

 in vain in the alluvial strata laid open in the delta of the 

 Mississippi at low-water for similar remains. In some of 

 the ancient fluviatile mud of the valley of the Mississippi, 

 which I have compared to the loess of the Rhine, land and 

 freshwater shells of existing species abound, but they must 



