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quantities in sand originating from sandstone. All these mine- 

 rals have less power of resistance against mechanical and che- 

 mical influences than the quartz, and disappear in the course 

 of time, partly during the hardening of the sandstone, partly 

 during its later erosion. As the ratio between these minerals 

 and the quartz is somewhat variable (generally between 5 and 

 20 per Ct. in primary sand, i. e. sand formed directly from 

 granite or gneiss), it is difficult to distinguish the primary from 

 the secondary sand (formed from sandstone), even if they are 

 found unmixed, but if they are mixed up it is impossible, even 

 approximately, to determine the percentages of each. 



Even if an examination of the sand does not give any 

 particularly good idea of the ratios between the individual rocks 

 which have contributed to the formation of the deposit, we may 

 yet obtain from it certain results, which would not be reached 

 by an examination of the rock- fragments in the sample. In the 

 first place these are abtogether absent in some of the samples, 

 or they are present in such small amounts that we cannot draw 

 any conclusions from them as to the ratio between the different 

 ingredients. Secondly it often happens that the sand has been 

 deposited in a quite different way from the stones, so that we 

 can draw no conjoint conclusion with regard to these. The 

 stones must have originated either from moraines or rocks at 

 the bottom of the sea, the sand must have been derived from 

 these same factors, or directly from land. The following statistics 

 will show that there is on the whole a close connection between 

 the different ingredients of the sample. The most essential differ- 

 ence is that the sandy ingredients are almost always particularly 

 rich in quartz, which circumstance is especially striking in the 

 samples in which the coarser ingredients consist totally of ba- 

 saltic material. In the samples from the south of Iceland 

 something of the same occurs , for quartz is hardly ever 

 quite absent in sand, even if it seems almost impossible for it 

 to be conveyed to the locality in question. The only explana- 



