196 Evolution and Distribution of Fishes 



aspect than the hard lime rock. The enclosed organisms 

 are of most diverse character, but whether plants, medusae, 

 brittle-stars, echinoids, leeches, worms, crustaceans, mol- 

 luscs, fishes, reptiles or birds the finer structural details are 

 revealed often in marvellous manner. Further as grouped 

 by Walther they may roughly be divided into water and 

 land forms. 



It becomes therefore a matter of special interest to 

 learn how such a deposit originated. Walther evidently 

 very correctly pictures, as a background setting and starting 

 point, the presence of a Kimmeridgean land-mass, into 

 which extends a lagoon or shallow arm of the Jurassic sea 

 that then covered large areas in Western Germany, France, 

 and East England. Coral reefs and islands dotted over 

 this sea, while through activity of the associated marine 

 organisms, those deep deposits of organic lime-carbonate 

 origin had formed which we know as the marine Liassic and 

 lower Oolitic strata. 



But Walther then pictures a constant tendency to ele- 

 vation and depression of the lagoon that now is the Wies- 

 enthal, with resulting death and stranding of the organisms 

 near the surface of each deposit, when such by elevation 

 became dried in the sun. The wafting of dark-colored land 

 debris — inorganic and organic — gave rise to the separating 

 films that now cause parting of the layers (or flinze). Re- 

 newed depression of the lagoon area started another limey 

 deposit over its surface, that lasted till renewed elevation 

 took place. Sudden death of the organisms was effected, 

 owing to and simultaneously with, volcanic changes that 

 caused the elevation. 



This view is an ingenious and attractive one, and further 

 seems well to fit the case, since Walther shows that the land- 

 derived animals were evidently mostly dead before being 

 embalmed in the strata, while the marine organisms — the 

 medusae, brittlestars, antedons, crustaceans, and some fishes 

 — were entombed in the living state. But for many reasons 

 the writer would suggest a different and much more efficient 

 explanation, one however which would doubtless have been 

 ruled out of court before publication of Russell's work. 



