in Testacea from the London Clay. 



379 



the drift bed into the London clay, the latter being penetrated to 

 the depth of 8 or 9 feet ; the shells being very abundantly dis- 

 seminated throughout. Barytes is of rather rare occurrence in 

 the London clay. In the list of the minerals of this formation 

 given in the ' Outlines of the Geology of England and Wales/ 

 it is not even mentioned. 



Phillips, in his ' Introduction to Mineralogy/ states that the 

 sulphate of barytes " occurs in crystals disposed in a radiated 

 form on carbonate of lime, coating the divisions of the septaria, 

 on the western side of the Isle of Sheppey." 



In the numerous specimens of Testacea and other organic re- 

 mains which I was so fortunate to obtain from the excavations in 

 the London clay at Primrose Hill, and from the deep cuttings of 

 the Great Northern Railway near Whetstone, I have not detected 

 the trace of any similar barytic substance, and the occurrence of 

 it in the locality previously mentioned may be probably due to 

 the condition of the clay in its upper part at that spot, being 

 more favourable to the decomposition and rearrangement of the 

 chemical constituents of the matrix itself and of the contained 

 organic bodies. 



EXPLANATION OF THE FIGURES. 



a,f, represent the deposit in an unbroken state within the apertures of a 

 Natica glaucinoides and a Fusus ; b, shows the space it generally 

 occupies within the shell; c, the deposit broken, showing two 

 centres of radiation ; d, g, i, Natica and Pleurotoma, containing 

 the deposit in a broken state, showing the fibro-radiate structure ; 

 e, h, umbilici of Natica filled with the deposit ; k, I, m, n, o, mag- 

 nified figures ; p, magnified figure of the deposit in the clay. The 

 natural size is represented in outline. 



