322 Evolution and Distribution of Fishes 



beds as the above two genera, C. bucklandi is one of the 

 many freshwater types of the Solenhofen Slates, and C. an- 

 drewsii occurs at a still higher level — the Lower Purbeck 

 beds — of the epoch. Brodie says regarding these that 

 "they rest on the Portland series" (255). The fossilif- 

 erous rock is a very fine-grained white shaly limestone of 

 laminated structure, and much resembling the Solenhofen 

 slate. The slabs "abound in Fish, Insects, impressions of 

 plants, Cypris, Archaeoniscus and rarely shells, most of 

 which belong to the genus Cyclas, and one species of Palu- 

 dina." 



The species which probably occurs highest in the geo- 

 logic scale, and which is of special interest geographically 

 is C. australis. It was described by Woodward from Tal- 

 bragar beds of N. S. Wales. Though there may be some 

 doubt attaching to the exact age of these, David, Jack, 

 Pittman, and Woodward agree that they are Jurassic rocks 

 laid down In depressions of Triassic strata {154)- 

 David and Pittman say: "The fishbeds proper form the 

 lowest of the three members into which, on lithological 

 grounds, the deposits to which they belong, may be divided. 

 They consist of laminated hard siliceous shales, cherty in 

 places, rendered ochreous by ferruginous infiltrations. . . . 

 Fish and plants are so abundant that it is difficult to find 

 even a small fragment of the shale devoid of them." They 

 further observe that "the fish-beds are succeeded conform- 

 ably by white siliceous shales, which do not appear to be 

 fossiliferous. They consist of silica in a very fine state of 

 division," and are about 15 feet in thickness. 



Woodward says: "The fishes are crowded together in 

 shoals as if suddenly destroyed and very few of them have 

 become disintegrated before fossilization. A glance at the 

 accompanying plates will show how beautifully even the 

 most delicate bones and fin-rays are usually preserved." 

 The writer would again suggest, as the only known explana- 

 tion of such conditions, that the fishes were killed by com- 

 bined shock, poisonous gaseous fumes and volcanic dust. 

 The last was in this case — unlike the Purbeck and Solen- 

 hofen slates noted above — a siliceous dust-shower. Then 

 after death and entombment of the fish, plant, and insect 



