154 
THE ItOCK ROOM* 
It is customary to unite the Lias with the overlying Oolites 
under the general name of the Jurassic system. The Case 
numbered 41 to 50 is devoted to the important group of Oolitic 
strata, which have been mentioned in an earlier part of this 
guide as yielding some of our valued building stones (p. 30), 
as well as the fissile limestones known as the Stonesfield and 
Colly weston “ slates ” (p. 36). The various sub-divisions of the 
oolites, from the Inferior Oolite to the top of the Purbeck 
series are well represented by rock -specimens in this series. 
The opposite Case, numbered in sections, 51 to 60, is set apart 
for illustrations of the rocks of the Cretaceous System. Com- 
mencing with the fresh- water beds of the Weald, which include 
the Hastings sand and the Weald clay, we pass thence to the 
marine beds of the Lower Greensand. Mention has already 
been made of the “Sussex marble” from the Weald clay 
(p. 31), as well as of the “ Kentish Rag ” from the Hythe beds 
of the Lower Greensand (p. 30). Passing upwards we meet 
successively the Gault clay, the Upper Greensand, and the 
Chalk. The eye will be attracted by the specimens of Red 
Chalk, a rock which occurs at the base of the White Chalk 
in the fine cliff-section at Hunstanton, in Norfolk, and is 
found also in Lincolnshire and Yorkshire. The varied forms of 
flint and the curious nodules of iron-pyrites claim attention ; 
whilst the visitor should also notice the hard varieties of 
chaik known as “ Melbourn Rock ” and “ Chalk Rock ” — the 
former occurring at the base and the latter at the top of the 
Middle Chalk. Here, too, are examples of the phospbatic chalk 
of Taplow, discovered a few years ago by Mr. A. Strahan. 
In the last Case, the compartments of which are numbered 61 
to 70, will be found a collection of typical rocks of Tertiary 
and later date. The large section across the London Basin, 
displayed in the upper part of this Case, may be advantageously 
studied in connexion with the examples of Eocene rocks. 
Specimens from th#^ Eocene, or Lower Tertiary, series are 
exhibited not only from the Metropolitan area but also from the 
Hampshire basin, including part of the Isle of Wight ; and with 
these may be associated the Tertiary basaltic rocks of the north- 
east of Ireland and the west of Scotland. Photographs of 
exceptional size and beauty, illustrating the characteristic 
scenery formed by the columnar basalt of the Giants’ Causeway, 
are suspended on the neighbouring wall. The Oligocene beds, 
more recent in age than the Eocene deposits, are represented by 
specimens from the fluvio-marine series of the Isle of Wight. 
It is now believed that strata of Miocene age are not present 
in Britain ; but the succeeding Pliocene period is represented, 
partly by the “ Crags,” or shelly sands, of East Anglia, and partly 
by certain fragmentary deposits at St. Erth, in West Cornwall, 
and at Lenham, in Kent. 
In illustration of the Pleistocene or Quaternary period there are 
here exhibited numerous specimens from the glacial drift, from 
