354 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 22, 



series), for 1866, of the ' Journal of the Chemical Society of Lon- 

 don,' records some important experiments bearing on the subject of 

 the colour of red beds. 



Professor Brush, of Tale College, U. S., in a paper on the '' Native 

 Hydrates of Iron," at p. 219 of the vol. for 1867 (new series, 

 no. xliii.) of the 'American Journal of Science,' describes the cha- 

 racters of several definite hydrous sesquioxides of iron, and also re- 

 fers to the investigations of Mr, Davies as doing away with the ne- 

 cessity of the supposition of great heat to account for the presence of 

 anhydrous haBmatite. 



Dr. J. Low, in a paper on the " Carstone of West Norfolk," read 

 before the British Association at Norwich, this year, attempts to ex- 

 plain the formation of ferruginous nodules in the white sands of 

 the Lower Greensand by the infiltration of ferruginous matter and 

 its segregation around organic substances. 



On the subject of the bleaching of ferruginous rocks by organic 

 matter, I would also refer to a paper by Kindler, published in * Pog- 

 gendorfiPs Annalen ' (vol. xxxvii. p. 203), and noticed in ' Bischof s 

 Chemical and Physical Geology' (vol. i. p. 166, English edition), 

 and also to Bisehofs own experiments on the reduction of sesqui- 

 oxide of iron to protoxide by organic matter (' Chemical and Physical 

 Geology,' English edition, vol. iii. p. 1), as bearing on the theory ad- 

 vanced by Dr. Dawson, but which seems to be only of limited ap- 

 plication in accounting for the variegation and discoloration of red 

 beds. 



2. The States of Combination of Iron in the pn'iicipal Stratified 

 Rocks. — To more readily describe the various forms of mottling and 

 variegation which are the subject of the following analysis, it will 

 be necessary to refer to the states of combination of the iron perva- 

 ding the principal stratified rocks as a colouring-matter. 



Yery prominent in connexion with the subject of variegation are 

 the red beds, including the Trias and Devonian, and also portions 

 of the Carboniferous, Permian, Tertiary, and other formations, 

 which are coloured with from 4 to 15 per cent, of the anhydrous 

 sesquioxide, and contain, also, small amounts of hydrous sesquioxide, 

 carbonate of protoxide, and silicates of iron. 



The following analysis, by Mr. David Forbes, of red clay occurring 

 as a stratum 7 or 8 feet thick at about the middle of the Shropshire 

 Coal-measures, maybe taken as representing the general composition 

 of the unaltered portions of many red beds that have been subject 

 to partial bleaching. 



Analysis No. 74. Eed " Tile Clay," Shropshire Coal-measures, 

 Calcotts, near Broseley. (The coarse particles had been previously 

 removed by passing the clay through a fine lawn sieve.) 



Silica combined, 29-71 1 aaha 



SHicafree, 34-35 J ^'^ 



Titanic acid 0-62 



Alumina 20-60 



Sesquioxide of iron 6*84 



Protoxide of iron 0*32 



Protoxide of manganese 0-09 



