ME. 47.] CYKENA. 133 



are found are 5 or 6 feet beneath the bottom of the pit, and 

 are only worked in winter. I had three trenches dug, but they 

 were not left open. M. Marcotte, a friend of M. de Perthes, 

 promised to collect for me all he could in the course of the 

 autumn or winter. There is no Pharmacien there who could 

 do it. 



If you have a trench dug, let it be near where my first 

 trench was. At the last two I had dug I found nothing of 

 importance. 



Of the sand itself you will find a good heap collected in one 

 part of the pit, and will find plenty of fresh-water and land 

 shells ; but various shells are very rare. I got a few fragments ; 

 but all my present specimens come from the first trench, so also 

 the Cyrena. 



As for the Cyrena, here we found it on Saturday week high up 

 in the section in Simpson's pit at Erith ; and you may remember 

 that Mr Meeson found a Gryphcea incurva in the ground quite at 

 the bottom of his pit at Grays. Was this from the Boulder 

 Clay ? I have never seen one in the Western Drift. As for 

 these two Drifts, after great work I imagined I had found the 

 latter superimposed on the former on the top of a hill near 

 Brandon ; whilst last year I found the Boulder Clay in a valley 

 near St Albans, with the Western Drift capping the hills flank- 

 ing this valley, and therefore apparently older than the B. Clay. 

 I must get a third case to serve as umpire. 



I think the Cyrena existed at the time of the ElepJias primi- 

 genius both at Erith and Menchecourt. Ilford and Grays I am 

 not certain about ; but I have my doubts. The fact is, we have 

 many places where the Cyrena occurs; but unfortunately from 

 all the elephants having been E. primigenius formerly, sufficient 

 information of the exact fact is now wanting, owing to many 

 specimens having been overlooked, and not collected, or lost. 



When you go to the Norfolk Cliffs, look again at Mundesley. 

 I have been there three times, and on each occasion came to the 

 conclusion that the shell- and peat -bed there was above the 

 Boulder Clay. On the last occasion I, however, found another 

 bed of shells under the B. Clay. 



As for the exact order of succession, it is so complicated 

 that, as often as I imagined I had detected it, as often have I 



