xi IMPERFECTION OF THE RECORD 141 



remains have been embedded being itself preserved during 

 the constant changes going on on the earth's surface, and 

 ultimately appearing in a situation accessible to man's re- 

 search. (3) What the further chances against their being 

 so found, even if they should have been preserved in an 

 accessible locality. 



I might refer you to the exceedingly minute portion of 

 the earth's surface which has yet been really explored 

 palseontologically ; to the cases that are occurring every day 

 of new and most unexpected forms and of whole species 

 or orders, known only by an isolated individual, as the 

 Archceopteryx of the Solenhofen oolite ; to say nothing of 

 more recondite speculations in the work above referred to, on 

 the improbability of preservation of intermediate forms, owing 

 to variation having usually been most rife during periods of 

 elevation, when fossilisation is less likely to occur. 



All these show in such a striking manner the extremely 

 small value of negative evidence in palaeontology, that I am 

 quite justified in asking you to leave it altogether out of 

 consideration in thinking of, or reasoning on, what is to 

 follow. 



Such being the material with which we have to deal, it 

 will be seen that we must go to work upon it in a most 

 careful and circumspect manner. We cannot rush at con- 

 clusions, but must be content cautiously, and often with much 

 labour and anxiety, to piece together our facts, scrupulously 

 observing the minutest hints, and following out the direction 

 indicated by often very obscure signs, before we can recon- 

 struct even an outline of the fabric from which we hope to gain 

 an idea of the past history of the beings of which we treat. 



I have selected for illustration of the subject this evening 

 the division or order of Mammals called by naturalists 

 UNGULATA, or hoofed animals, chiefly because it is the one 

 of which the paleeontological history at least in the tertiary 

 period (for beyond that we cannot trace it) is better known 

 than any other, and as that of which the classification, that 

 is, the relations of its various sub-groups to each other, is 

 on the whole better understood than in most other zoological 

 divisions. 



