54 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



The average analysis of Col. 2 has been calculated, on the assumption that 

 the alkalies are referable to the orthoclase and albite molecules and the iron 

 oxides to magnetite. All of the lime is referred to the carbonate. The result, 

 noted below, is probably not far from representing the actual composition of 

 the rock. 



Orthoclase 34-47 



Albite 3-14 



Quartz 6-00 



Magnetite 6-26 



Magnesium carbonate 21-17 



Calcium carbonate 28-60 



99-64 



Half of the rock is composed of the two carbonates, in which the ratio of Ca 

 to Mg is 1-87: 1, indicating but a very slight excess of calcium over that found 

 in normal dolomite. The remainder is chiefly silicious, especially feldspathic 

 matter. The rock is apparently unique among analyzed dolomitic sediments in 

 showing such a high percentage of potash. This alkali is without doubt contained 

 in the orthoclase, which is probably somewhat sodiferous. The concentration of 

 so much of this feldspar in a dolomitic sediment is hard to understand. If the 

 microscopic relations permitted the view that the orthoclase, like the feldspars 

 of the Altyn beds, were of clastic origin and derived from a granitic terrane, 

 one would still be at a loss to understand the relative poverty in quartz. The 

 suggestion due to optical study, that the feldspathic material has really been 

 introduced in solution offers obvious difficulties but seems to be a more pro- 

 mising hypothesis to explain the presence of most of the feldspar. This more 

 probable view itself suffers from the doubt arising from the fact that the rock 

 shows no evidence of having been recrystallized or notably metamorphosed, as 

 we might expect if it had been penetrated by solutions to the extent demanded. 

 A third hypothesis, that, under special conditions, the potash was introduced 

 into the original carbonate mud in the form of the soluble aluminate of 

 potassium, which during burial and lithifaction, reacted with dissolved silica 

 in the mud-water to form orthoclase, is perhaps worthy of mention; but it faces 

 the obvious objection that no conditions in nature are known by which the 

 aluminate is formed from the potassium salts in sea-water. Another sugges- 

 tion may be drawn from the fact that isomorphous mixtures of calcium and 

 potassium carbonates can be prepared in the laboratory. If such isomorphic 

 mixture were thrown down from the sea-water of the Waterton time, the one 

 constituent of the orthoclase would be added to the mud but the presence of 

 alumina in its exact proportion to potash (and soda) would be hard to explain. 

 Finally, as suggested to the writer by Professor C. H. Warren, the presence of 

 so much alkali may possibly be due to the original precipitation of glauconite in 

 the mud, in which the feldspar was formed by recrystallization under peculiar 

 conditions. In view of its obvious difficulties the problem of this extraordinary 

 rock must be left unsolved. 



