36 ADDRESS TO THE BRITISH ASSOCIATION, 1881. 



twelve periods, in each of which by far the greater 

 number of species were distinct. True, the number of 

 species was probably not so large in the earlier periods 

 as at present ; but if we make a liberal allowance for 

 this, we shall have a total of more than 2,000,000 

 species, of which about 25,000 only are as yet upon 

 record ; and many of these are only represented by a 

 few, some only by a single specimen, or even only by a 

 fragment. 



The progress of palaeontology may also be marked 

 by the extent to which the existence of groups has been, 

 if I may so say, carried back in time. Thus I believe 

 that in 1830 the earliest known quadrupeds were small 

 marsupials belonging to the Stonesfield Slate ; the 

 most ancient mammal now known is Microlestes 

 antiquus from the Keuper of Wiirtemberg : the oldest 

 bird known in 1831 belonged to the period of the 

 London Clay, the oldest now known is the Archaeop- 

 teryx of the Solenhofen Slate, though it is probable 

 that some at any rate of the footsteps on the Triassic 

 rocks are those of birds. So again the Amphibia have 

 been carried back from the Trias to the Coal-measures ; 

 Fish from the Old Red Sandstone to the Upper Silurian ; 

 Reptiles to the Trias ; Insects from the Cretaceous to 

 the Devonian ; Mollusca and Crustacea from the 

 Silurian to the Lower Cambrian. The rocks below the 

 Cambrian, though of immense thickness, have afforded 

 no relics of animal life, if we except the problematical 

 Eozoon Canadense, so ably studied by Dawson and 

 Carpenter. But if palaeontology as yet throws no light 

 on the original forms of life, we must remember that 

 the simplest and the lowest organisms are so soft and 



