THE GEOLOGY OF CROYDON. 
One among the many interesting objects of geological enquiry, 
is the attempt to restore, or realize in idea, the conditions under which 
the various sedimentary strata constituting the surface of the globe 
were formed, Buried, as some are, under newer sediments, their 
edges only seen, perhaps altered by long continued physical 
changes, and portions partially removed, are occurrences which 
perfect as the geological record frequently is, and though the line of 
involve the enquiry in some difficulty, but leave it still of interest. Im- 
j 
continuous. 
being produced. 
shown in the following descending order :— 
Pleistocene—Gravel ..........ccesecscscncncnteereeeeesteseenees ) 
Eocene—London Clay, Oldhaven or Blackheath Beds, ; Tertiary. 
Woolwich Beds, Thanet Sands ............00esee8+ 
Cretaceous—Upper, Middle, and Lower Chalk ...... «. Secondary. 
continuity in certain areas is broken, this imperfection may be 
compared to a volume in which sometimes leaves and sometimes 
whole chapters are destroyed, but which in other and separate volumes 
are more perfectly preserved, so that the story or history is 
This, to some extent, is found to be the case in studying the 
geology of Croydon ; for although the strata in this locality are 
apparently continuous, yet, between certain portions of them, there 
is good evidence (based upon geological knowledge) of a long lapse 
of unrepresented time, during which, in other areas, thick marine 
accumulations were taking place and great physical changes were 
I propose, therefore, to treat the geology of Croydon as a 
means, not only of explaining the origin of the strata here, but of 
showing their relations to the strata forming the London basin, as well 
as to other and more distant districts. The rocks which constitute 
the crust of the globe, are chiefly of Igneous and Aqueous 
formation; around Croydon they belong to the latter division, 
and consist of gravel, sands, clays, and chalk, which are either of 
marine or estuarine origin. Geologists have divided the water- 
formed, or sedimentary rocks, into three great periods, dependent 
on the peculiar forms of ancient life found in them or on their 
relative positions, namely—Primary, or Paleozoic ; Secondary, or 
Mesozoic ; Tertiary, or Kainozoic. See Section, Fig. 4, p. 27. 
Now the beds in this neighbourhood belong to the later portion 
of the second and to the earlicr part of the upper period, as 
