48 Evolution and Distribution of Fishes 



It seems possible, therefore, that by invoking the aid 

 of such agencies, the origin, structure, and richly fossilifer- 

 ous nature of many bone beds, fish beds, and related strata 

 can be explained, for where multitudes of entire fishes are 

 preserved as perfectly as in a museum, the volcanic dust 

 probably fell as these were being destroyed by mechanical 

 concussion, by poisonous gases, or by super-heated waters, 

 possibly even through clogging with dust of the gills. If 

 such destruction occurred — as we hope to show actually did 

 happen in fresh-water lakes or swamps, or in shallow seas 

 whose bottoms became elevated either during death of the 

 fishes or soon after, the continued fall of dust would im- 

 mediately cover and seal them up. As the oily constituents 

 of the fishes exuded, and as increased pressure of the ashy 

 material took place, simultaneously with drying of the 

 dust deposits in the sun, the oil would aid in preservation 

 if sufficiently rich, while the deposits of ash, gradually 

 hardening by chemical action and reaction as above de- 

 scribed, would render permanent the preservation process. 



Where, as in the Downton deposits of England and the 

 Corniferous deposits of America, an intermingled mass 

 of teeth, scales, spines or jaws mainly make up the "bone- 

 bed," the soft dead bodies of great shoals of fishes killed in 

 some sudden manner as above described, had undergone con- 

 siderable decay in some shallow, freshwater lagoon. While 

 decay of the flesh took place an abundant discharge of oily 

 constitutents occurred, the harder parts became separated 

 and dropped into the volcanic ash, where they were, by 

 pressure and chemical action, condensed into a solid mass. 

 The discharged oily materials receive consideration below. 



Such an explanation seems to afford a complete key to 

 many hard fissile beds of Old Red Sandstone. Thus those 

 described by Flett {22; 383) in the Orkney Isles and by a 

 A. Geikie (2j; 399) for Dunnet Head, are cases in point. 

 Though we would not press the matter unduly at this stage, 

 it even affords a likely reason for the origin of many beds 

 of ironstone, that in the States, in Canada, and in various 

 parts of Europe, are so often encountered in sections of 

 Old Red and of Carboniferous age, not to say in later 

 deposits. The often abundant embedded or interlaminated 



