INTRODUCTION. 



TO THB 



GUIDE TO THE FOSSIL* INVERTEBEATA IN THE 

 GEOLOGICAL DEPARTMENT. 



Before visiting tlie Geological Galleries upon the east side, it 

 is very desirable that the student should have seen and become 

 acquainted with the recent Zoological collections on the west 

 side of the entrance ; and, if he would properly understand the 

 structures and characters of animals, he should spend some time 

 in studying the beautiful series of objects in the Introductory 

 Collection, which occupies the cases in the bays or recesses on 

 each side of the great Central Hall. 



As an introduction to the Geological Galleries a few words 

 are needed. Geology embraces the investigation of everything 

 connected with the formation and history of the earth which 

 we inhabit, both organic and inorganic. In the Mineralogical 

 Gallery, on the east side, upon the first floor, will be found a 

 very complete exposition of specimens illustrating the nature and 

 properties of rocks and minerals forming so large a part of the 

 earth's crust; but in the Geological Galleries the exhibited series 

 is necessarily confined to some illustrations of the sedimentary 

 and organically - formed rocks, arranged stratigraphically in 

 Gallery XI, and to as complete a series as possible of the re- 

 mains of the animals and plants which have been entombed in 

 the various deposits which compose the ground beneath us. 



These rocks and sediments and the organisms found in them 

 are of very different relative ages (see the Table of Strata), some, 

 like the Cambrian and Silurian, being extremely ancient, and 

 containing only invertebrate forms of life, the species of which 

 are now quite extinct ; others, like the Eocene strata, being 

 very rich in remains of all classes of organisms ; whilst the later 

 Tertiary deposits often yield abundant evidence of animals very 

 nearly related to those which are living at the present day. 



