A HALF-CENTURY OF SCIENCE. 79 



gards as a character inherited from reptilian ancestors ; the ichthyor- 

 nis, stranger still, with biconcave vertebra?, like those of fishes, and 

 teeth set in sockets. 



As giving, in a few words, an idea of the rapid progress in this 

 department, I may mention that Morris's " Catalogue of British Fos- 

 sils," published in 1843, contained 5,300 species ; while that now in 

 preparation by Mr. Etheridge enumerates 15,000. But, if these figures 

 show how rapid our recent progress has been, they also very forcibly 

 illustrate the imperfection of the geological record, and give us, I will 

 not say a measure, but an idea, of the imperfection of the geological 

 record. The number of all the described recent species is over 300,000, 

 but certainly not half are yet on our lists, and we may safely take the 

 total number of recent species as being not less than 700,000. But in 

 former times there have been at the very least 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 paleontology 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 quadru- 

 peds were small marsupials belonging to the Stonesfield slates ; the 

 most ancient mammal now known is 3icrolestes antiquus from the Keu- 

 per of Wurtemberg ; the oldest bird known in 1831 belonged to the 

 period of the London Clay, the oldest now known is the archceopteryx 

 of the Solenhofen slates, 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 be- 

 low the Cambrian, though of immense thickness, have afforded no 

 relics of animal life, if we except the problematical Eozobn Canadense, 

 so ably studied by Dawson and Carpenter. But, if paleontology 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 perishable 

 that they would leave "not a wrack behind." 



Passing to the science of geography, Mr. Clements Markham has 

 recently published an excellent summary of what has been accom- 

 plished during the half-century. But the progress in our knowledge 

 of geography is, and has been, by no means confined to the improve- 

 ment of our maps, or to the discovery and description of new regions 

 of the earth, but has extended to the causes which have led to the 

 present configuration of the surface. To a great extent, indeed, this 



