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were accustomed to walk on damp surfaces of sand or mud open to 

 the air, and the impressions left by their feet were afterward dried in 

 the sun, before the waters flooded anew, overspread them with layers 

 of sediment, in a manner that now annually takes place during the va- 

 riations of the seasons on the broad flats of the Great Salt Lake of 

 Utah and in other salt lakes. The occurrence of pseudomorphs of 

 crystals of salt in the Permian beds of the Vale of Eden also helps 

 to this conclusion, together with ripple-marks, sun-cracks, and rain- 

 pittings, impressed on the beds. Crystals of common salt were not 

 likely to have been deposited in an open sea, for, to form such crys- 

 tals, concentration of chloride of sodium by evaporation is necessary. 

 Deposits of gypsum, common in the Permian marls, could also only 

 have been formed in inland waters by concentration, or on occasional 

 surfaces of mud exposed to the sun and air, for no reasonable explana- 

 tion can be offered of a process by means of which sulphate of lime 

 can be deposited amid common mechanical sediments at the bottom 

 of an open sea. 



The question now arises how to account for the formation of the 

 bands of magnesian limestone, sparingly intermingled with the red 

 marls and sandstones of Lancashire and the Vale of Eden, and of that 

 more important limestone district in the eastern half of the north of 

 England, forming a long escarpment between Tynemouth and Not- 

 tingham. In these we have a true but restricted marine fauna, inter- 

 mingled, however, with the relics of Amphibian and terrestrial life. 



Let us broadly compare the marine life of the preceding epoch, 

 that of the Carboniferous Limestone series, with the fossils of the Mag- 

 nesian Limestone. The marine fauna of the Carboniferous Limestone 

 of Britain contains about 1,500 species, most of which are mollusca 

 (869), corals (124), echinodermata, Crustacea (149), and fish (203). 

 The Permian fauna feebly resembles that of the Carboniferous epoch, 

 but, instead of the vast assemblage of many kinds of life found in the 

 latter, the Magnesian Limestone of England only holds nine genera 

 and 21 species of Brachiopoda, 16 genera and 31 species of Lamelli- 

 branchiata, 11 genera and 26 species of Gasteropoda, one Pteropod 

 (Theca), and one Cephalopod (Nautilus). The whole comprises only 

 38 genera and 80 species, and all of these are dwarfed in size when 

 compared with their Carboniferous congeners, when such there are. 



I cannot easily account for this poverty of numbers and dwarfing 

 of the forms, except on the hypothesis that the waters in which they 

 lived were uncongenial to a true ocean fauna ; and in this respect the 

 general assemblage may be compared to the still more restricted ma- 

 rine faunas of the Caspian Sea and the Sea of Aral, or rather to that, 

 a little more numerous and partly fossil, of the great Aralo-Caspian 

 area of inland drainage, at a time when these inland brackish lakes 

 formed part of a much larger body of water. Some of the fish of the 

 Marl-slate have strong generic affinities with those of Carboniferous 



