GENEEAL AEKANGEMENT OF ITS CONTENTS. 
21 
and the extensive series of reptiles, fishes, and other animals 
preserved in spirit, are kept for the purposes of safety in a 
separate building behind the Museum. In the Botanical 
Department the reserve collections are kept as usual in the 
well-known form of an Herbarium or Hortus siccus. 
The great bulk of the specimens being arranged in these Supplement- 
three series, there might still be supplementary collections for 
facilitating the study of the distribution of animals and plants, 
and perhaps also of minerals, in space and in time. The first, 
constituting a geographical series, might show by illustrative 
examples the leading characteristics of the fauna and flora 
of each great region of the earth's surface; the second, or 
geological series, would give examples of the fossil remains 
found most abundantly in each formation, arranged as far as 
may be in chronological order. 
The only attempt hitherto made at exhibiting a geographical Geographical, 
series in the Museum is the special collection of animals of the 
British Isles, arranged in a room on the ground floor behind the 
great staircase of the Central Hall. It would be impossible in 
the present building to find room for any further geographical 
collections, however interesting and instructive they might be. 
With regard to geological collections, although the specimens Geological, 
in the department so called are mainly arranged not geologi- 
cally, or according to stratigraphical position, but according 
to their natural affinities, yet, in many cases, it has been 
found convenient to adopt a mixed arrangement, the specimens 
within each large natural group being classified according 
to the sequence in age of the strata in which they were 
found. Such an arrangement however is only applicable to the 
fossils of a particular region, owing to the great difficulties 
in accurately determining the correspondence in age of forma- 
tions occurring in distant parts of the earth's surface ; hence 
a large and varied paleeontological collection, such as that of 
the British Museum, must be arranged in the main upon a 
systematic or zoological and botanical basis. A limited but 
instructive series, showing the most characteristic rock forma- 
tions with their included fossil remains, of the British Isles, 
placed in chronological sequence, is arranged in one of the 
galleries of the Geological Department. 
