JoLY — An Estimate of the Geological Age of the Earth. 51 



This brings us face to face with the question as to where and in what form 

 this missing potash is to be sought. 



Tlie Glauconite deposits of the deep-sea boundaries and the stratified marine 

 sediments undoubtedly must be chiefly made responsible. The comjDosition of 

 this substance is given in the Report on the Deep Sea Deposits of the "Challenger " 

 Expedition, where it is shown that it contains from 2-52 to 4-21 per cent, of potash 

 derived from the sea-water. It may amount to 50 per cent, or 60 joer cent, of the 

 shallower deposits, or even more. The percentage of soda is from \ to -Jy of the 

 potash, and therefore will hardly enter into consideration in this j^aper. 



The formation of this substance appears dependent on the condition that the 

 organic matter in the chambers of Foraminifera should reach the bottom, which, 

 if so, will perhaps account for the absence of this body from the deeper deposits. 

 The organic matter " transforms the iron in the mud into sulphide, which may be 

 oxidised into hydrate, sulphur being at the same time liberated : this sulphur 

 would become oxidised into sulphuric acid, which would decompose the fine clay," 

 (terrigenous debris), " setting free colloid silica, alumina being removed in 

 solution; thus we have colloid silica and hydrated oxide of iron in a condition 

 most suitable for their combination." " There is always a tendency for potash to 

 accumulate in the hydrated silicate formed in this way, and, as we have stated 

 before, this potash must have been derived from the sea-water."* 



The following extract (page 38i) will serve to show the opinions of the 

 authors (Sir J. Murray and Professor Renard) on the widespread nature of this 

 deposit : — 



" It has already been stated that glauconite is one of the minerals most widely 

 distributed in sedimentary rocks. It is found in the primary formations of Russia 

 and Sweden among sands and gravels, in the Cambrian sandstone of North 

 America, in the Quebec Group of Canada, and in the coarse Silurian sands of 

 Bohemia. In the secondaiy formations its presence is more pronounced ; for 

 example, in the Lias, and especially in the middle and upper layers of the 

 Jurassic system in Russia, in Franconia, in Swabia, and in England. It has a still 

 greater development in the sands, marls, and chalks of the Cretaceous formation. 

 It will suffice to recall the glauconitic rocks of the Neocomian, of the Gault, and 

 of the Cenomanian in various regions, such as the glauconitic marls of France, 

 Germany, England, and several parts of North America. The abundance of 

 glauconite is continued into the Tertiary formations, from the lowest up to the 

 highest horizons of the series. 



" From this rapid enumeration, it is seen that glauconite traverses the whole of 

 the geological periods, and its formation is continued in modern deposits along 

 many continental shores, explored by the ' Challenger ' and other expeditions." 



* Eeport, p. 389. 



