THE FDIST RAINS — HADDING 291 



the oldest known strongly diflferentiated rocks. I find it therefore 

 lo<Tically correct to draw the conclusion from the })roniiscs given 

 in the quoted material that the leptite formation is formed on the lli'bt 

 appearance of liquid water in the earth. 



The reasons of the above-mentioned conclusion may be summed 

 up as follows: 



1. Normal subaquatic sediments are found in several places in 

 the younger part of the Archaean. We can easily follow the sedi- 

 mentary series of strata in a more or less metamorphic sha[)e down 

 to the Lower Archaean. In this then Ave have to look for the oldest 

 sediments. 



2. The Lower Archaean is nowhere easier of access than in Swe- 

 den. Therefore we may expect to find traces of the oldest sedi- 

 ments in the Lower Archaean of Sweden. 



3. liocks of sedimentary origin occur in the Swedish leptite 

 formation, which we consider as the upper part of the Lower 

 Archaean. These rocks are partly strongly differentiated (above 

 all limestone and iron ores), partly undifferentiated, of pyroclastic 

 origin. 



4. It has not been possible to show any rocks of sedimentary origin 

 in the part of the Archaean that is older than the leptite formation. 



As to the progress of formation we may add : 



5. Before the condensation of the water the earth's surface was 

 to a large extent covered with loose volcanic ash, which was bound 

 only by juvenile gases and lava beds. 



6. By the ai)pearance of liquid water the ash was formed into 

 enormous quantities of tuffs, that soon came to enclose leaching 

 products also, above all lime and iron compounds. The chemical- 

 mineralogical differentiation was gradually accomplished by normal 

 weathering and sedimentation. The pyroclastic roclis then became 

 less conspicuous and normal sediments dominated. 



We may sum up the argument thus: The details are debatable but 

 only one opinion on the process as a whole and its general results is 

 possible. From this point of view we must conclude that the leptite 

 formation ctmtains the oldest sediments of the earth, and that these 

 were formed in connection with the first condensation of the water. 



SOME MORE PROBLEMS 



Though I have now discussed the problem of nearest interest to 

 me I can not forbear to mention a few more that are directly con- 

 nected with this. One of them concerns the question : How far back 

 in the earth's history does the first appearance of the water lie? 



We are accustomed to use large figures when stating the age 

 of rocks belon«;ing to one formation or another. These fiirures are 



