﻿434 DR. G. T. MOODY ON" THE CAUSES OF [Aug. I905. 



Keuper Marl from Aust Cliff. 



Green portion. 



Fe 2 3 0-87 



FeO 143 



Bed portion. 

 320 

 112 



CaO 744 



MgO 126 



6-13 

 090 



C0 2 7'46 



6-23 



Water lost at 100° Oentigr. 4*31 

 Si0 2 56-46 



4-96 



55-08 



A1 2 3 13-52 



1416 



Undetermined .. 7*25 



8-22 



100-00 



100-00 



These analytical results place beyond doubt the fact that the 

 red portion of a variegated rock contains a higher 

 percentage of iron and lower percentages of calcium- 

 carbonate and magnesium-carbonate than the green 

 portion ; and they are in agreement with the observation of Maw 

 that red strata are usually less calcareous than adjacent green strata. 



Two hypotheses, in explanation of the difference in composition 

 of the parts of variegated rock caused by infiltration, are possible. 

 The first is that the green rock may have been formed by the 

 removal of ferric oxide from, and by the addition of lime and 

 magnesia to, the rock. The second is that the green rock may 

 have been converted into the red rock by the addition of ferric 

 oxide, and by loss of lime and magnesia. 



The first hypothesis was advanced by Maw, and it is necessary 

 to consider if, and to what extent, such an exchange of lime and 

 magnesia for ferric oxide in the red rock is possible. The removal 

 of ferric oxide from a red marl necessarily involves previous 

 dissolution of the iron. The dissolution might be brought about, 

 either by exchange of the basic portion of some soluble salt for 

 ferric oxide, or by direct dissolution of the iron-oxide in acid. 

 Experiments were made with the object of removing the iron either 

 partly or entirely from the red marl, by passing through it solutions 

 of calcium- and magnesium-salts, including the sulphates, chlorides, 

 and bicarbonates. Calcium-bicarbonate and magnesium-bicarbonate 

 were prepared by aerating saturated lime-water and magnesia 

 suspended in water, respectively, in a ' sparklet '-syphon. The 

 resulting clear solutions were subsequently forced by their own 

 pressure through glass Soxhlet tubes containing the powdered marl. 

 In all these experiments negative results were obtained, not a trace 

 of iron going into solution. 



The action of acids on the red marl was next studied. The marl 

 in fine powder was placed in beakers, made into a stiff paste with 

 water, and solutions of acid of approximately-normal strength were 

 added drop by drop, with constant stirring. It was found in every 

 experiment that no iron passed into solution, so long as any of th& 

 magnesium-carbonate or calcium-carbonate of the marl remained 

 undissolved. The addition of acid without stirring, leading to- 



