100 
the resemblance to the fossils of Potton is such that nearly all 
Potton types of life have already occurred at the Wicken dig- 
gings. Potton however is rich in vertebrate remains and in the 
phosphatic casts of shells; at Wicken the silico-phosphatic con- 
cretions are smaller, and the mollusca, &c. for the most part 
preserve their carbonate of lime shells; moreover at Potton have 
occurred Cycadoidea microphylla, Cycad cones, cones of Pan- 
danus and three species of Pinites, besides much wood mineral- 
ized, sometimes with phosphate of lime, sometimes with silex. 
At Wicken but little wood has occurred. All these facts appear 
to demonstrate that, assuming the phosphate beds at these places 
to be one and the same, then Potton was nearer to the old land, 
streams from which brought down the animals and plants, than 
was Wicken. This was assumed. Then it would follow that 
on these deposits being traced to the south-west they would 
become fluvio-marine and freshwater, and finally have no repre- 
sentative in that direction because of the interposition of dry 
land. Also if these remains were brought down by rivers (and 
they are in the same state of preservation as bones from the 
Wealden), the river banks on ceasing would become continuous 
with the sea shore of the land, along which would be distributed 
fragments of the rocks which formed the cliffs in those days, as 
well as rolled bones. 
Such a pebble bed is found, and with it are mixed the 
nodules of phosphate of lime, the casts of shells, the sand nodules 
concreted with phosphate of lime, and most of the reptilian 
remains. The pebbles are chiefly old rocks, black slate, Lydian 
stone, brown hornstone, white and rose quartz, with an occa- 
sional fossil from the mountain limestone, notably joints of the 
column of Poteriocrinus. 
And it would also follow that on these deposits being traced 
out at sea parallel to the shore the pebbles would cease, the 
sands would become fine and thin, and ultimately be replaced 
by clay ; moreover, assuming a small river to have brought down 
