22 



cence of these organic tracings. Several beautiful diagrams 

 illustrated this part of tlie paper. 



That many flints are sponges or organic structures, permeated 

 with silex, is very evident, but to endeavour to account for the 

 formation of flint entirely on a theory of organic origin cannot 

 be received as satisfactory. Any theory to be complete must 

 explain all the facts in connection with the presence and appear- 

 ance of flint. No hypotliesis of the organic origin of flint 

 sufB.ciently explains the oblique tabular layers of flint which 

 pass thi'ough beds of chalk that must have taken ages to attain 

 their great thickness, for sponge, &C., could not grow in one 

 succession for these countless ages; the re- cementing with 

 sUicious matter, fractured and displaced surfaces of crushed 

 flints ; the banded structure of some flints resembling onyx ; or 

 the chalcedonic structure tilling cavities. 



Mr. Dowker then explained in much detail these several con- 

 ditions of flint alluded to, quoting from the papers of Woodward, 

 Wetherell, Tomlin Smith, and his own, and illustrating them 

 from the abundant excellent sj)ecimens on the table. Our limits 

 •will not permit us to do full justice to these remarks. In none 

 of these varied states did organic structure appear to be more 

 than accidentally present. The landed flints presented alternate 

 dark and white bands, generaUj^ arranged at right angles to a 

 given axis, when exposed to weather these bands resist unequally, 

 the softer wearing away and giving a ribbed appearance to the 

 stone, the ridge forming more or less complete circles. These 

 coloured bands, for they do not appear to be always white, are 

 due to infiltration. Flints are known to be porous and to freely 

 absorb fluids from without, thus they are specially liable to be- 

 come stained with the colour of iron or chalk dissolved in such 

 fluids. The white, the yellow, and the green coats extending to 

 some depth are due to this, and, from all parts not beiag equally 

 porous, the tracings of organic structure are often distinctly 

 defined by the absorption of these coloured fluids from without 

 and their arrest around the structure. This banded appearance 

 is not confined to nodidar flints but was also foimd in the verti- 

 cal tabiilar layers of flint. At the junction of the Tertiary Beds 

 with the chalk in Kent, remarkable rccemented flints are often 

 met with. They present many fractures that have been reunited 

 with silicious matter, the surfaces often having shifted and 

 joined in a new position. In some cases between the surfaces 

 intervenes a layer of white coated flint. Various casts of fossils 

 found in the chalk occur, as Ananchites, Spatangus, Cidaris, 

 Galerites, Lima, and Ventrictdtes, presenting the features of the 

 original surface of the fossil, and most wonderfully preserving 

 aU the delicate markings. This flinty substance not only filled 



