4 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
STlJATlGltArHlCAL SElilES AND HISTOiaCAL 
COLLECTIUNS. 
Gallery XI. Hanging on the wall of Gallery XI, immediately to the 
left of the entrance is a diagram shoving very broadly the 
Geological Epochs during which the rocks found in Great 
Britain were formed, the newest being at the top and the 
oldest at the bottom of the column. A more elaborate list, 
with the Epochs divided into Ages, is given as a table 
(facing p. 1) in the present Guide. 
Wall-cases Adjoining the diagram, in the wall-eases on the west side 
of the gallery, is the Stratigraphical Series, which is a 
collection of the various kinds of rock found in Britain, 
arranged in order of age. Along the top of the Cases is a 
diagram showing the succession of these rocks from the 
newest to the oldest, as they might be .seen in a continuous 
section across the country from east to west. Examydes ot 
the rocks themselves occur on the shelves below, where will 
also be found numerous small sections of the strata, as 
observed in various parts of England. Affixed to the Cases 
is a series of small mayis, each coloured to show the tract of 
country occuyiied by the one or two rock-groups of which 
syiecimens are exhibited in the adjoining Case. In the long 
section, the numbers yilaced beneath the beds give their 
ayiproximate thicknesses in feet. It must not, however, be 
suyiposed that all these beds occur in such regular succession 
right through the country, the fact rather being that one is 
found in one district, while another is better developed 
elsewhere, as indeed may often be gathered from the names 
ayiplied to the beds. Certain gaps in the section, as between 
Pliocene and Eocene, and again between Permian and the 
Coal Measures, reyiresent intervals of time, during which 
there were being deposited rocks, which are found in other 
parts of the world, but for one reason or another do not occur 
in the British area. 
It is jdain that when rocks have been deyjosited, lus we 
know that they now are being deposited, at the bottom of 
the sea, then the underlying rocks are older than those above 
them. As concrete examydes of the way in which one layer 
of rock is found lying on another, there aie placed on the 
door between the Wall-cases in various parts of the Gallery 
several examples of the cores of rock brought uy> from below 
Between by deep borings. Thus at Dover the boring for coal went 
Wall-eases down throuah the Chalk at tlie surface, through several rocks 
3 & 4 . ® 
