1868.] 



MAW VAKIEG ATEI) STRATA , 



:J8i5 



Analyses, 



No. G9. 



Red marl. 



8-96 



0-76 



0-12 



* Magnesia 



Potash 



Soda 



Sulphuric acid none. 



Carbonic acid and loss 1586 



Insoluble siliceous matter : — 



Silica 36-72^ 



Alumina 4-35 



Lime 0*15 



Magnesia 0*43 



Oxides of iron 0*53 



Alkalies and loss ... 1-33^ 



No. 70. 



Grey marl. 



7-60 



013 



002 



none. 

 22-763 



No. 71. 



Red band. 



18-52 



0-42 



009 



0-13 



36-765 



43-51 



26-54^ 

 2-83 

 0-30 

 0-23 

 0-36 



0-08; 



30-34 



9-26 

 mostly Silica. 



100-00 



100-00 



100-00 



In this section the change of colour seems to have been brought 

 about by a combination of mechanical and secondary causes. The 

 amount of iron decreases upwards from the red to the grey beds ; but 

 the curious freckled disposition where the grey and red colours inter- 

 lace is evidently 7iot the result of sedimentary arrangement, and ap- 

 pears to be connected with the infiltration of lime from the overlying 

 calcareous bands, and a secondary bleaching of a uniformly red bed. 

 Fig. 16 (PI. XII.) represents a section of some Permian strata in a 

 cutting of the Severn Valley Railway, between Linley and Bridg- 

 north, including red marls overlain by a calcareous band, in contact 

 with which the red marls have been discoloured of an ochreous 

 grey ; the interlacing disposition of the yellowish grey and the red, 

 with an ii-regular boundary of separation, shows that the former is 

 a secondary product of the original uniform red colour. 



The composition of the red marl (Analysis No. 4, by Dr. Yoelcker) 

 is as follows : — 



Wat«r of combination 2*79 



Sesquioxide of iron 3*23 



Protoxide of iron 1 '35 



Bisulphide of iron 0'02 



Carbonate of lime 4'15 



Sidphate of lime 017 



Alumina , 3-95 



Magnesia 2-17 



Alkalies and loss 1-22 



Matter (exclusive of the iron) insoluble in hydro- 

 chloric acid 80-95 



100-00 

 The composition of the ochreous yellow marl (Analysis, No. 3, 

 by Pr. Yoelcker) : — 



Water of combination 1-38 



Sesquioxide of iron 6482 



Protoxide of iron 0309 



Sulphur 0-039 



Equal to Carbonate of Mag- No. 69. No. 70. 



nesia 14-40 14-36 



and Magnesia in a state of 



silicate 2-10 0-76 



No. 71. 

 28-43 



4-41 



2e2 



