THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



No. 84. APRIL 1844. 



XXX. — On the Zoological condition of Chalk Flints, and the pro- 

 bable causes of the Deposit of Flinty Strata alternating with the 

 Upper Beds of the Cretaceous Formation. By D. T. Ansted, 

 M.A., F.R.S., Professor of Geology in King's College, Lon- 

 don, and Fellow of Jesus College, Cambridge. 



The occurrence of siliceous bands — the silex being exhibited in 

 detached fragments called flints — regularly bedded with the upper 

 portion of the Chalk formation in many parts of Europe has always 

 been considered a geological phsenomenon very difficult to ac- 

 count for, and the explanations hitherto offered have been ex- 

 tremely unsatisfactory, because they have assumed a mineral con- 

 dition for the silica which we are not warranted by experience in 

 supposing to be possible, and which no one who fairly examines 

 all the circumstances of the deposit can at all conclude to be 

 probable. 



Dr. Buckland has supposed, for instance^!^, that each new mass 

 of calcareous and siliceous matter as it was discharged formed a 

 bed of pulpy fluid at the bottom of the then existing ocean, and 

 that the separation of the siliceous from the calcareous ingre- 

 dients was modified by attractions drawing the particles to cer- 

 tain centres. Dr. Mantell again in 1833 remarks t, speaking of 

 a specimen of Ventriculite, " the appearance of this specimen 

 seems to warrant the conclusion, that at the period of its minera- 

 lization the silex was in the state of a thick viscid fluid.'' And 

 in 1838 Mr. Lyell, referring to Dr. Buckland's account already 

 quoted, adds, " Nevertheless the separation of the flint into lay- 

 ers so distinct from the chalk is a singular phsenomenon, and not 

 yet accounted for. Perhaps, as the specific gravity of the sili- 

 ceous exceeds that of the calcareous particles, the heavier flint 

 may have sunk to the bottom of each stratum of soft mud." 



I need hardly say more in illustration of my remark, that the 

 origin of flints in chalk is a phsenomenon not yet satisfactorily 

 explained : nor, indeed, do I venture to assert that the view I 



* Geol. Trans. 1st series, vol. iv. p. 422. The date of this paper is 1816. 

 \ Geol. of South-east of England, p. 102. 

 Ann. ^ Mag. N. Hist. Vol. xiii. R 



