114 W. A. Richardson—The Relative Age of Concretions. 
connected with the main part of the Paris Basin by a large number 
of outliers, but along the shores of the English Channel there are 
other outliers (at St. Valery-sur-Somme, Montreuil, etc.), forming 
a connecting chain with the deposits of Northern France. 
Summarizing the geographical conditions in the whole region at 
the time of formation of the Hocene strata, there was a single large 
basin stretching from Norfolk on the north to beyond Paris on the 
south, and from Devonshire on the west to the Limburg (Hastern 
Belgium) on the east. This basin may have been enclosed, but was 
more probably open to the north-east. Sediment was being poured 
into it from two principal sources—by a great river flowing eastwards 
into the basin in the London and Hampshire regions, and by another 
river emptying northwards in the Paris region. Subsidiary sources 
of sediment probably lay to the east in Belgium. It is hoped that 
a study of the detrital minerals, at present being carried out by the 
author, will throw further light on this subject. Throughout the 
period the basin was subjected to earth-movements, of which the 
gradual but intermittent uplift of the Wealden Dome seems almost 
certainly to have been oneresult. This caused a periodic transgression 
and regression of the marine waters of the basin, and so it is only in the 
centre that one would expect to find a succession of marine deposits. 
Round the periphery one should have, if conditions for preservation 
were ideal, a succession of continental deposits. Over the greater 
part of the whole region one has a succession of marine and con- 
tinental deposits in regular alternation, and the beds can be grouped 
naturally into a series of cycles of sedimentation. As will be shown 
later, the same cycles are traceable over the whole basin, and it is 
essential to consider the four areas—France, Belgium, London, 
and Hampshire—as a single region. 
(To be continued.) 
The Relative Age of Concretions. 
By W. Aurrep Ricuarpson, M.Sc., B.Sc. (Eng.), F.G.S. 
I. Tue ReELative AGE. 
(Meas age of a concretion, relative to that of the parent-rock, must 
be either :— 
1. Contemporaneous.—The concretion grew on the sea-floor at 
the same time, and at about the same rate, as the surrounding deposit 
was laid down. 
2. Penecontemporaneous.—The concretion segregated more or 
less close to the surface of recently deposited sediment. 
3. Subsequent—The concretion formed after deposition had 
finished, and after the strata had largely consolidated, but, perhaps, 
before cementation had taken place to any noteworthy extent. 
Further, if the concretion were formed subsequently to the main 
deposit its attitude to the mother-rock must have been either :— 
