Geological Activities of Marine Micro-organisms 27 



our experiments in one or the otiicr way by using more fa\ orablc 

 conditions, or we have to restrict ourselves to reproduce and to 

 join single episodes of a long geological process. 



It is obvious that these methods are more speculative and 

 that the conditions of a model experiment must be discussed 

 in every respect. On the other hand, we cannot renounce these 

 methods. The value of geomicrobiological ideas can only be 

 established if we try to take both paths. 



