The Geology of Devizes. 



Bound way, Etchilhampton, and near Eastcott. At the last place it 

 contains further evidence of its siliceous character in yielding* hard 

 cherty nodules which may be regarded as imperfectly formed flints. 

 These, too, correspond closely with nodules that are found in the 

 Malmstone of Surrey, but no such objects have ever before been 

 found in Chalk, so that Wiltshire can claim them as a unique 

 phenomenon. 



The structure of this siliceous Chalk is illustrated in Fig. 3 ; 

 which is made up of two parts of a slide of such Chalk, and shows 

 the various states of mineralization exhibited by the sponge spicules. 



e 



f 



a 



Fig. 3. Structure of Siliceous Chalk (magnified about one hundred times). 



The general ground mass is seen to consist partly of globular silica, 

 partly of shell fragments (/.) with still finer calcareous dust between 

 them i a is a sponge spicule the central part of which is filled with 

 globular silica; b b are spicules of unaltered silica cut through 

 obliquely and showing the axial canal filled with Glauconite ; c is 

 a partly dissolved spicule — its outline only shown by the globular 

 silica into which it seems to have passed ; and d is another partly 

 destroyed spicule ; e is a grain of Glauconite, of which this slide 



