200 Proceedings of the Royal Society of Edinburgh. [Sess. 
physical peculiarities of the adsorbent, but also, and especially, with the 
specific adsorbability of the element itself. On comparing the percentage 
in Red Clay with the concentration in sea- water, the order of adsorbability 
is found to run K, Ca, Mg, Na, the latter element being a very bad fourth ; 
this sequence exactly reverses that of abundance in sea-water. Evidence 
that these elements are held by adsorption is furnished by the fact that 
they can be extruded to some extent by neutral salts of a more adsorbable 
base, such as ammonia. By means of dilute acid, which partially breaks 
down the clay aggregate, still more adsorbed matter is set free. The sub- 
joined figures show (a) the percentage of certain constituents, in hydrous 
form, in No. 4 ; (b) the amounts extracted by boiling for a few minutes with 
seminormal hydrochloric acid ; and (c) the amounts extracted in the same 
way by 3 per cent, ammonium sulphate : — 
a. 
b. 
c. 
ai 2 o 3 . 
14*43 
4*18 
Fe 2 0 3 
6-28 
3-59 
CaO ... 
0-65 
0-60 
0-36 
MgO 
2-60 
1-15 
0-41 
k 2 o ... 
1-48 
0-66 
033 
The tendency of soils and clays to adsorb potash and magnesia has long 
been known, and has been investigated quantitatively by Van Bemmelen. 
In the deep sea a very striking case of potash-adsorption in palagonite 
was directly demonstrated by Murray and Renard.* 
Continental clays which have been in contact with sea- water or other 
saline medium commonly retain small percentages of calcium and magnesium, 
which sometimes puzzle analysts owing to the absence of sufficient 
carbonic acid to account for their presence as carbonate. j- The opportunity 
may here be taken of remarking that Brazier’s habit of stating magnesia 
as MgC0 3 in all deposits, £ which has led more than one naturalist into 
speculations on dolomitisation, cannot be regarded as justifiable, at any 
rate for the less calcareous deposits. 
In all probability retention of potash by bottom-deposits (by no means 
necessarily as glauconite) has something to do with the secular impoverish- 
ment of the ocean in potash, relatively to soda. It is well to remember, 
however, that if Red Clay is a deposit formed in situ , the adsorbed potash 
* Challenger Reports , “ Deep-Sea Deposits,” p. 307. 
t Cf. Vesterberg and Manzelius, Bull. Geol. Inst. Upsala, v., No. 9, p. 125, 1900. 
J Challenger Reports , “ Deep-Sea Deposits,” passim. 
