400 Geological Memoirs. 



appeared not necessary to assume any subaqueous action and subse- 

 quent elevation, or any subsequent covering by water, since they most 

 resembled the great rubbish heaps near Cahira in Egypt and else- 

 where, which exhibit the same appearance of regular stratification, 

 and have been formed without water. 



The idea therefore of a relation between volcanic action and the 

 conditions of existence of the most minute organic beings ceased to be 

 a mere vague speculation, and some proof of its correctness was 

 presented by gradual successive steps in investigation. 



On his return from his summer excursion, the author found an 

 admirable and systematic collection from his correspondent at Bonn. 

 The first glance of these under the microscope showed their nature, 

 and the investigations at Hochsimmer have gradually led to the 

 following results. 



The infusorial polishing slate occurs on the eastern slope of the 

 Hochsimmer (about four miles from the Laacher-See), between the 

 roads which branch off from Ettringen to St. Johann and Waldesch. 

 It is interstratified between beds of pumiceous conglomerate. 



Immediately under the vegetable soil we find — 



feet. in. 



1. Ferruginous pumiceous conglomerate 8-10 



2. Volcanic tuff 1 



3. Infusorial stratum (polishing slate) 2-3 



4. Finely-grained pumice conglomerate 2-3 



5. Coarse pumiceous conglomerate which has 



been penetrated to a depth of. 3 6 



Total thickness 12 ft. 4 in. to 15 ft. 



The lower pumiceous conglomerate evidently reposes on the grau- 

 wacke, which with clay-slate forms the underlying deposit in the 

 neighbourhood. The beds of volcanic conglomerate which enclose 

 the infusorial polishing slate have a considerable dip, amounting to 

 20° north-west, and their thickness appears in some places to amount 

 to as much as twenty-four feet, but the bed of polishing slate 

 uowhere exceeds three inches. The upper covering seems to form 



