During Triassic and Jurassic Periods 173 



again are stated to be mixed up with Myophoria, Lima, 

 and Terebratiila. But on p. 62 under Upper Silesian Keu- 

 per he notes that: "The few organic remains belong to 

 a freshwater fauna, which consists unitedly of amphibians 

 (Mastodonsaurus) , saurians {Termatosannis) dipnoans 

 (Ceratodus) , ganoids {Colohodtis and Saurichthys) , 

 freshwater mussels and snails {Anoplophora, Paludina) y 

 So the former probably was recorded from a thin band of 

 rock, of freshwater origin deposited during some land 

 oscillation, between marine beds. This view is entirely in 

 accord then with the finding of Colohodtis and Saiirichthys 

 in both lists. 



Another, and at first sight puzzling, development is 

 that of the bone-beds of England, of Mid and North Ger- 

 many, of North Italy and elsewhere. These occur at the 

 junction of the Rhaetic with the Keuper below, or in the 

 Rhaetic, or as in the Wurtemburg bone-beds, at the junc- 

 tion of the Rhaetic and the Lias. It is not unlikely that 

 one of these bone-beds at least may represent one continuous 

 stratum, for in England and over a large part of the Eu- 

 ropean continent, the Rhaetic bone-bed seems always to 

 adjoin an extensive marine deposit, whose most abundant 

 fossil is Aviciila contorta. So it is known as the "Avicula 

 contorta" zone. In the bone-beds proper occur Ceratodus 

 latissimus (altus), C. parvus, C. silesiacus, the teeth or 

 spines of Acrodtis minimus, Hybodus minor and H. laevius- 

 cidus, as well as bones of reptiles. Either above, or in close 

 proximity, are beds with abundant plant-remains. 



Now all of the above genera of fishes, as well as the 

 associated organisms, belong to groups that in the palae- 

 ozoic rocks are clearly freshwater. The probable explana- 

 tion is that though marine beds may be near to or ad- 

 joining each bone-bed above or below, the latter was formed 

 on a land surface owing to some sudden and comparatively 

 short-lived upheaval of what had been a marine bed. Soon 

 thereafter and as a nearly concomitant event, terrible and 

 widespread destruction of freshwater fishes caused strand- 

 ing of these on top of the upheaved marine beds. These 

 fishes then underwent decay during deposition of the mud 

 or micaceous clay that now surrounded them. So their 



