162 Prof. Ehrenberg on the Origin of the Paramoudras. 



deed sponges), and among these, along with many imperfect 

 specimens, some well-preserved microscopic Polythalamia, 

 shells, and Infusoria, of the same species which I have found 

 diffused in like manner in all flints from the chalk, and which 

 therefore very probably may have had great influence at the 

 formation of these very extensive layers of stone. I also readily 

 recognised well-preserved exoxa^XeifiiXanthidiumpilosum and 

 fragments of X, ramosum*, together with the Polythalamia, 

 which I have mentioned in my memoir on the Berlin flints. 



The sinking of this silica, deriving its origin from organic 

 fragments, by its own gravity, in a funnel shape, through a more 

 solid but naturally still soft layer of chalk, may probably be 

 explained from local circumstances (perhaps from air cavities), 

 which caused the yielding of the yet soft subjacent chalk, 

 where large horizontal flat masses of silica had collected, and 

 could in its pulpy state still sink in the form of a funnel, 

 when the superior layer of chalk pressing down on it formed 

 the core. A heavier body coming from the upper layers of 

 chalk may also have here and there slowly sunk through the 

 soft siliceous masses into the under layer of chalk, and have 

 left these flint funnels behind as indicators of its passage. In 

 the first case, the funnel would always be found closed .at the 

 bottom ; in the latter open at the top and bottom. In each case 

 it would always be wider at the top and narrower at the 

 bottom. If the flint funnels stood with their wider aperture 

 directed downwards, a penetrating force may have proceeded 

 from below upwards, and in this way ascending gases may 

 have operated. Local observations will easily explain further 

 this interesting phaenomenon. The circumstance of the other 

 contemporaneous forms of the English layers of flints being for 

 the greater part compressed in flattened plates, speaks against 

 the supposition that they were well-preserved sponges in which 

 Infusoria and MoUusca happened to be living ; and also the 

 remaining upright of such large soft forms is not at all pro- 

 bable J nor does the existing internal structure in any way fa- 

 vour this view. Ehrenberg. 



• Drawings of these two as well as of several other species of Xanthidium 

 occurring in tlic English flints will be found in the plates illustrating the 

 Kev. J. 15. Rcadc's Paper in the present number. — Edit. 



