248 Evolution and Distribution of Fishes 



had been suddenly killed, and that they were subsequently 

 enveloped by snow-white limestone. Had there been no 

 violent action it would be difficult to explain how such quanti- 

 ties of these larvae could have been buried in the rock, some 

 in a running, others in a resting position, with the mask, 

 extended or retracted." In the next higher bed the dragon- 

 flies disappear, but numerous remains of the white-fish 

 Leuciscus are now found. 



Heer then considers that "a rising and sinking of the 

 ground," which might be due to volcanic agency, probably 

 took place, since a volcanic rock occurs "that resembles 

 the phonolitic and basaltic tuffs of the neighboring Hohgau. 

 Further "it is manifest that the volcanoes of the Hohgau 

 were in activity at the same time with those of Oeningen." 



While agreeing with much of the valuable and original 

 information contained in these volumes, not least that 

 quoted above, the writer nevertheless would give a different 

 interpretation to some of the phenomena presented. As 

 to the origin of much of the richly fossiliferous rock- 

 substance, and specially the numerous thin lamellae noted, 

 he would regard such as intermittently successive deposits 

 of volcanic lime-dust laid down in the course at most of 

 a few years. The source of this dust Heer sufficiently 

 accounts for in his mention of the not far-distant volcanoes. 

 In conjunction with this we must bear in mind that huge 

 thicknesses of limestone strata were on every side and had 

 to be broken through, caught up periodically in the volcanic 

 vents, and ground to powder there before being extruded 

 (p. 44) as a fine almost impalpable powder, which alike 

 in air, when rain-exposed, or under water, would speedily 

 set into the hard thin lime lamellae described. 



Heer's suggestion that the land rose and fell in inter- 

 mittent manner, and so caused alternate drying and flooding 

 of the region, is in line with much that has been described 

 as an accompaniment of volcanic disturbances and would 

 undoubtedly aid in perfect preservation of the enclosed 

 organisms. All of these did not decay, and break up loosely 

 in freshwater that was slowing depositing sediment. After 

 being spread out in water, or after being suddenly killed 



