340 Evolution and Distribution of Fishes 



group of freshwater beds that enclose the extensive sets of 

 plants, fishes, reptiles and other organisms which have 

 rendered the beds famous. Above the bituminous schists, 

 but continuous with them, are the lithographic slates that 

 closely resemble those of Solenhofen-Eichstadt, and are 

 according to Thiolliere and his successors of the same age 

 and mode of deposit, but which at Bugey are rather poor in 

 organic remains. 



The writer would interpret the Bugey deposits as fol- 

 lows. Soon after deposition of the Ostrea virgiila beds 

 along a.seabeach or bank, extensive volcanic disturbances 

 occurred that elevated the land and converted a large area 

 into an extensive but shallow lake, which extended at least 

 from W. Bavaria to near the present Rhone. This became 

 surrounded by a typical Jurassic vegetation, and a group 

 of crocodilean and saurophidian reptiles, while the waters 

 became stocked with a typical freshwater fish life of the 

 period. Then came a volcanic outburst, some dozens of 

 miles distant, but which destroyed life over a wide area, 

 and deposited a thick layer of volcanic dust, over the lake 

 and its environs. At Solenhofen fish life had been some- 

 what scant, and the fishes along with other organisms were 

 gradually killed and mixed up in the dust deposits as these 

 successively were laid down. So the strata are only faintly 

 bituminous. 



In the Bugey area as has so often happened under like 

 conditions, great shoals of the fishes had been killed and 

 piled on each other during the earlier period of eruption. 

 From these oozed out later the copious products which 

 by subsequent analysis became the intrinsic rock petroleum. 

 After destruction and entombment of these fishes, of the 

 reptiles, and of the plants, continued deposit of volcanic 

 dust in zones that alternated with thin zones of other 

 detrital debris, represented probably alternating periods 

 — a day or two only it may have been — when changes in 

 wind currents occurred. For a few hours or longer the 

 winds may have carried the volcanic dust, then for a few 

 hours it may have veered and fitful gusts may have de- 

 posited fine debris of aeolian character from higher ground 

 around. 



