dl 
March 4, 1867. 
The PrestpEnt (H. W. Cookson, D.D., Master of St Peter's 
College) in the Chair. 
On Roslyn or Roswell Hill Clay-pit, near Ely. By the 
Rev. O. Fisoer, M.A., F.G.S. 
Rostyn or Roswell Hill Clay-pit has long been a standing 
puzzle to Cambridge geologists. I have visited it several times, 
and have notes upon it made in 1853 and 1856. I was there 
in November of the present year, having by Professor Sedg- 
wick’s permission the assistance of H. Keeping. 
The pit is probably well known to you. It covers several 
acres of ground, and extends in a direction N.W. and 8.E. The 
material has been used for the purpose of making up the 
banks in the fens, and the section is comparable to that of 
many natural cliffs. 
The northern side of the pit is occupied by horizontal Kim- 
meridge clay, which is or used to be capped here and there by. 
a thin covering of lower green sand. At the western end of 
the pit boulder clay of a typical character abuts against the 
Kimmeridge clay, the plane of junction running nearly east 
and west, and dipping at a high angle under the boulder clay. 
The southern side of the pit, as at present exhibited, shows a 
blueish grey cretaceous clay, flanked at either end by nearly 
vertical chalk marl, which becomes somewhat argillaceous 
towards the eastern end of the pit. The chalk marl and clay 
are evidently in true sequence. 
The question which I propose to discuss relates to the sin- 
gular collocation of these several beds. 
I will first of all consider the presence of the chalk marl 
and the clay on the northern side of the pit. 
I have said they are clearly in sequence. Their junction is 
perfectly natural. The chalk marl becomes sandy, and contains 
