TRANSACTIONS OF SECTION C. 573 
that the evidence afforded by the materials of the gravels points conclusively to 
their derivation as fluviatile deposits mainly from the Bunter sandstone of the 
North and West Midlands, but débrzis from the harder Jurassic strata of the 
Mercian region is common, along with rolled fragments of crystalline rocks (of 
uncertain derivation) and small sarsens, with much flinty material from the chalk. 
They are referred to the period of the great Miocene continental elevation ot 
North-Western Europe, when rivers from the Welsh border and the Derbyshire 
highlands probably flowed across a ‘ peneplain’ to join the great arterial Tamisian 
line of drainage of Southern England, through valleys in the chalk marked (e.g.) 
by the gaps at Hitchin and Elsenham. Recent deep well-sections at the latter 
place and at Bishop’s Stortford prove that the valley of the Stort is a buried 
valley of erosion in the chalk, and probably continuous with the similar buried 
valley of the Cam, These.stratified gravels are conceived to be indexes of the 
work done by rivers, as sub-atmospheric denudation proceeded during the Miocene 
period of elevation, and before the present Mercian chalk escarpment was de- 
veloped, the presence of Jurassic débris in the gravels telling us that the Mercian 
rivers had cut their way by erosion down to the Jurassic rocks. 
The present Mercian river system owes its inception probably to the develop- 
ment of a slight anticlinal flexure running roughly 8.W. and N.E. in Pliocene 
times, letting in the waters of the North Sea to deposit the E. Anglian Crag on the 
one side, and originating the depression of the area of the Wash drainage, as 
indicated by the dip of the strata seen in the cliffs at Hunstanton. The easterly 
trend of the Mercian rivers thus brought about is considered to be the main factor 
in the development of the Mercian chalk escarpment. The evidence of the early 
Neogene age of these stratified gravels may be thus summed up: (i.) They are 
of fluviatile origin, and their materials show that they were brought across the 
Mercian region ; (ii.) no rivers could have laid them down where we find them, 
with present surface-contours ; (iii.) they are older than the boulder clay of the 
district, which everywhere overlies them, with a pretty sharp definition ; (iv.) they 
are older than Stort Valley, which is itself a line of erosion cut into the chalk to a 
depth of nearly 200 feet ; (v.) in one place (at Stansted) they are seen by faulting 
to have partaken in earth movements affecting the chalk and Reading beds. 
9, Some Remarkable Occurrences of Struvite Crystals. 
Ly Dr. Huew Marswaty, /R.S. 
10. On the Occurrence of Pebbles of White Chalk in Aberdeenshire Clay. 
By A. W, Gres. 
The record of the Cretaceous period in the North-east of Scotland is a very 
fragmentary one. The principal traces hitherto noted consist of a deposit of the 
nature of a Greensand—not proved to be in situ—at Moreseat, Cruden, and large 
numbers of flints scattered over the surface of the ground in the same locality 
between Buchanness and the Hill of Dudwick. 
Further indications of Cretaceous strata have recently been found at Strabathie, 
in the district of Belhelvie—about five miles north of A berdeen—in a bed of lami- 
nated clay close to the sea, The clay is found to contain pebbles of white chalk 
in considerable abundance. Some of the pebbles measure nearly a foot in length, 
but the majority are small. Some of them inclose flints. That they have been 
worn off an adjoining land surface is shown by the fact that numbers of them are 
markedly glaciated, and that pebbles of other rocks, identical with or similar to 
the rocks of the district, are found in the same pit. These facts indicate that 
Upper Cretaceous beds have once been, and perhaps somewhere are still, in situ 
in the locality. 
It has been ascertained by boring that the clay deposit covers a considerable 
area, and, as fresh exposures are constantly being made in the process of working 
the bed, further finds may be anticipated. 
