35 



PAPER BY A. S. REID, Esq., ON THE FORMATION 

 OF RED ROCKS. 



^lay 5th, 1880, 



..,-H ^\u- K- ?'''^.' ^-r- °^ '-'• J°^"'« ^°'I<^ff^' Cambridge, 

 £t:lJ^^ 1 ^^'',.s<^^™entary rocks in England are the red 

 spates of the Lower Cambrian, the red sandstones of the Old 

 Red Sandstones, the basement and top beds of the carboniferous 

 formation the greater part of the Permian and Trias, the red 

 chalk of Hunstanton and Specton. and the red crag of the East 

 .ZT'^ ■ .'hese are coloured by the same pigment, the red 

 peroxide of iron, but the method of its introduction is different 

 m different rocks. Putting aside rocks that are coloured red by 

 nu^ans of over-l^ing rocks or from being derived from the de- 

 composition of hornblendic rocks, &c., v;e may make three 

 classes. (1) Prof. Ramsay has shown that in infanTseas and 

 lakes red sediments are hkely to be formed by the evaporation 

 of bicarbonate of iron in contact M^ith the air. and its pfedpita" 

 tion in the form of peroxide, which as an insoluble red sediment 

 forms a film round the quartz granules of the sandstone ?r "s 

 intermingled with the argillaceous material of shales The 

 HrVr'T..''^ "PP^^-'"^'-k'/oot-prints, sun-cracks, and worm 

 tracks and the occurrence of pseudomorphs after rock salt, and 

 thick beds of sal and gypsum, all point to inland sea condit ons 

 while the unfossihferous state of the beds or the occurrence of 

 a dwarfed manne fauna help to establish the fact that the -reater 

 thickness of the rocks enumerated above was deposited in inland 

 lTk"J^"^T^ ^'^ J-^" Challenger investigations have ho'vn 

 us that a red clay is being formed at the present dav in depths 

 greater than 2,d00 or 3,000 fathoms in our Oceans. This deposi? 

 IS derived either from the decomposition of volcanic materSls 

 or the ultiniate residue of foramenifera tests, dissoTed by 

 carbonic acid. (The method of deposition of this sediment^ 

 &c, was described ) Some geologists consider the red slaves of 

 h^ ?h '\'?K ^'^"^'"' -'■^"P *° have been deposited thus 

 the author of the present paper considers that the fact that the; 

 a e interstratafied with grits militates against this theory. ProT 

 Sir CVVyville Thomson is inclined to believe " from a con- 

 sideration of their structure and embedded organic remSns that 

 none of the old formations were laid down at so grea^ depths " 

 borne of the Cambrian beds were, however, laid down at great 

 depths. Deep sea crustaceans are often either blind or have 

 abnormally large compound eyes to adapt them to thdr gloomy 

 life A genus of tnlobites (.^^:glina) occurs in the Areni? 3 

 of England possessing extremely large eyes; and J. E?Marr 

 F^G.S mentions the fact that in Bohemia, in beds of MenevtS 

 age. there are two species of liloenus, of which the one possess^ 

 huge compound eyes while the other is totally blind. ^ 



•.i,!u r^ u^!'^'^ of Hunstanton was probably homotaxial 

 with the Cambridge Greensand or nearly so ; this latter roc? 's 



