370 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 22, 



senting former cracks and cTiannels of infiltration ; and wherever 

 they cross the horizontal lines on which the isolated grey patches 

 occur, the particular position of each is evidently determined by the 

 intersection of the hard seams along which the grey patch branches, 

 as shown in fig:. 44. 



Fig. 44. Bleached patch in Keuper 

 Marls, Railiuay Cutting, Wor- 

 cester. 



A somewhat similar case oc- 

 curs in the red marls interstra- 

 tified with the white Keuper 

 sandstone in the Alderley cop- 

 per-mine, Cheshire. Pockets 

 or seams of the white sand oc- 

 casionally run down from the 

 sandstone into the marl (fig. 

 10, PL XI.), and adjacent to 

 these seams the red marl is dis- 

 coloured ; and similar bleached 

 marl bounds the line of separa- 

 tion of the red marl and sand- 

 stone-beds (fig. 11, PL XI.). 



Again, the position of a grey patch amongst the red is frequently 

 determined by a sHghtly harder condition of the stratum in a 

 particular part. The variety of circumstances that have deter- 

 mined the position of these discoloured bands and blotches, and the 

 variety in the character of the beds that are similarly afi'ected, show 

 that the phenomenon is quite independent of original diiferences in 

 the chemical composition of the red and grey parts of the strata ; 

 this is confirmed by the following complete analyses of the red and 

 grey parts of the Keuper Marls, Worcester Station, that have been 

 made for me by Dr. Yoelcker: — 



Analysis, 

 ^^o. 58, Eed. No. 



Water of combination 4'45 



Protoxide of iron 1"60 



Sesquioxide of iron 241 



Bisulphide of iron 0-059 



Alumina , 11-14 



Lime , , 485 



Magnesia 306 



Potash 0-69 



Soda , traces 



Sulphuric acid 0-09 



Carbonic acid and loss 3'311 



Matter insoluble in hydrochloric acid ; — 



Alumina .' 9-39^ ll-72> 



Sihca 53-62 53-40 



Oxides of iron weighed as sesquioxide 0*78 (^.Qof 0-99 



Lime 0-64 f''^'^^ 0-61 



Magnesia 1-69 1-11 



Alkalies and loss 2-22; 1-66J 



100-00 



59, Grey. 



3-71 

 1-77 

 0-80 

 0029 

 12-77 

 3-71 

 2-17 

 0-71 

 0-02 

 0-08 

 4-741 



69-49 



100-00 



The two examples contained but slight traces of carbonaceous 



