III. ТЬе mineralogicai constitution of the samples. 



As the samples of this expedition contain comparatively 

 large quantities of coarse ingredients, it has been possible to 

 determine the nature of the rocks that enter into the samples 

 with much greater accuracy than is generally the case. The 

 examination of the minerals contained in the sand, which is 

 generally of the greatest importance, is here of only secondary 

 moment. It is evident, that much more can be discovered by 

 an examination of the rocks, than by examining the sandy material. 

 Many rocks such as slate and limestone, are very rarely found 

 in the grains of sand, as they are very easily dissolved and 

 shattered when reduced mechanically to a very small size. The 

 same is the case with basalt, though in a much slighter degree. 

 With regard to this rock, an examination of the sand will al- 

 ways give good results , when only a comparison between the 

 different samples is wanted. Sandstone and quartzite, which in 

 these samples play a rather prominent part, will in the sand 

 become grains of quartz which cannot be distinguished from that 

 which originates from the granite. It is therefore only possible 

 to distinguish the sand formed by these rocks by the granitic 

 sand containing a small, but rather varied amount of other 

 minerals such as felspar, garnet, hornblende etc., which mine- 

 rals are found either not at all or only in quite insignificant 



