258 G. J. HINDE. — SILICEOUS ROCK FROM THE BOULDERCLAY 3l JUI1 



GEOLOGICAL HORIZON. 



Most of the spicular forms briefly referred to above, are widely dis- 

 tributed in Cretaceous and tertiary sponge-beds, and the majority of 

 them also resemble those of existing sponges,so thatit isnotpossible to 

 make any précise détermination frcm ihem as to the exact geological 

 horizon, from which they have been derived. In gênerai appearance the 

 material very nearly resembles the fine powder contained in many of 

 ihe larger flints from the upper beds of the Chalk with flints, which 

 occur, more particularly in the Chalk of Norwich, England, and near 

 Belfast in Ireland, and as it is now found in this boulder clay 

 commingled with flint fragments, there is reasonable ground for 

 supposing, that it may have formed part of the Upper Chalk of 

 Denmark. 



Croydon, 21 March 1889. 



