BY THE PEESIDENT. 117 



constructing their skeletons of flint, and the spicules in the interior 

 of white flint are very beautiful objects under the microscope. 

 They also testify to the probability of a great portion of the flint 

 in chalk having been originally organic. I think some investiga- 

 tions might be carried on to ascertain how far any of these diatoms 

 may be traced in our flint, and also to ascertain how far the 

 dissolution and formation of flint may be going on at the present 

 day ; for water has the power of dissolving a very minute amount 

 of flint, and under certain circumstances of parting with that flint. 

 If, for instance, water, with a certain amount of flint in solution, 

 gets into the interior of a flint, there seems a difiiculty in its 

 getting out with the flint in solution, and therefore it deposits it 

 in minute layers in the interior. I have no doubt you have noticed 

 in the interior of hollow flints those beautiful pieces of chalcedony 

 like bunches of grapes, and if you examine them under the micro- 

 scope, you will find that they have been deposited in layers by the 

 infiltration of water containing flint in solution. In some cases, 

 instead of the flint being deposited in thin films, it has been 

 deposited in crystals, and there is a curious change observable 

 occasionally, in which the flint, having been deposited in crystals, 

 after a certain length of time seems to change its character, and is 

 deposited in films over the original crystals, and on breaking the 

 chalcedony the crystals are seen like radii through the circular 

 protuberances. 



There are various pieces of geological work which may be done 

 in the neighbourhood. There is one interesting deposit in the 

 Chalk to which Mr. "Whitaker has given the name of the " chalk 

 rock." It comes about the middle of the Chalk, midway between 

 the Upper and Lower Chalk, and consists of a very hard rocky 

 stone, which may be seen on the railway in the neighbourhood of 

 Berkhampstead projecting from the sides of the cutting in large 

 blocks, and it is often met with in sinking wells a little to the 

 north of Watford. The shells of the organisms in it are distinct 

 from those in the chalk above and below it ; so that it seems to 

 have been deposited under somewhat different conditions. It 

 would be interesting to you to find how far the chalk rock 

 extends, at what depth it is, and to examine the organisms to be 

 found in it. The best locality is the pit on Rough-down in the 

 neighbourhood of Boxmoor Station, where I have found the 

 greater number of the shells characteristic of this chalk rock. 



Another geological subject which lies before us is to form some 



