692 KEroET — 1884. 



the position in the geological sequence is ascertained : in short, that horuotaxis of 

 marine, fresh-water, and terrestrial forms implies geological synchronism. 



That, as a general rule, homotaxis affords evidence that beds exhibiting it 

 belong approximately to the same geological period appears supported by a large 

 amount of evidence. But there are some startling exceptions. I propose to notice 

 a few typical instances, several of them Indian, in which the system of determining 

 the age of various formations by the fauna or flora has led to contradictory results, 

 before attempting to show wherein the source of the error appears to lie. Nothing: 

 would be gained and much time would be lost by entering upon the details of all 

 the cases known, even if I were able to give authentic particulars, which is doubt- 

 fid. It 'will be sufficient to cite some characteristic examples, concerning the 

 details of which satisfactory evidence is forthcoming. 



Pikermi Beds. — There are but few fossiliferous deposits on the face of the earth 

 that have attracted more attention than the Pikermi beds of Greece. In one of the 

 most classical and famous sites of the world, a few miles east of Athens, just 

 where 



The mountains look on Marathon 

 And Marathon looks on the sea, 



some red, silty beds occur, abounding in vertebrate remains. Some of the bones 

 were described by Wagner and others, but for a complete account of the fauna we are 

 indebted to Professor Albert Gaudry, who has himself collected by far the greater 

 portion of the remains hitherto procured. The following is a list of the genera 

 determined ; it is unnecessary to give the specific names :— 



MAMMALIA. 



Primates. — Mesopithecus, 1 sp. 



Carniyora. — Simocyon, 1; Mustela, 1; Promephitis, 1; Ictithevium, 3; 



Hycenarctus, 1 ; Hycena, 1 ; Hyceyiictis, 1 ; Felis, 4 ; Machccrodus, 1. 

 Proboscidea. — Mastodon, 2; Dinotherium, 1. 

 Ungtti'.ata. — Chalicotherium, 1 ; Rhinoceros, 3; Acerotherium, 1 ; Leptodon, 1 ; 



Hipparion, 1 ; Sus, 1 ; Camelopardalis, 1 ; Helladotherium, 1 ; Orasius, 1 ; 



Paltfotragus, 1 ; Protragelaphus, 1; Palaoryx, 2 ; Tragocerus, 2 ; Palccoreas, 1 ; 



Antidorcas (?), 1 ; Gazella, 1 ; AntUope, 3 ; Dremotherium, 2 ; Cervus, 1 . 

 TioDENTiA.— Mus (Acomys), 1 ; Hystrix, 1. 

 Edentata. — Ancylotherium, 1. 



AVES. 

 Phnsiamis, 1 ; Gallus, 1 ; Gen. gcdlinac. indet., 1 ; Grus, 1 ; Gen. ciconidar, 

 indet., 1. 



EEPTILIA. 

 Testudo, 1 ; Varanus, 1. 



Of mammalia alone there are known from this deposit 33 genera, of which 22 

 are extinct, and 47 species. 



Now, this fauna is almost invariably in European works quoted as Miocene. Of 

 the species found no less than 14 — Simocyon diaphorus, Ictitherium robnst.um, 

 I. hipparionum, Hyeena eccimia, Jiycenictis gr<rca, Machccrodus cidtridens, Mastodmi 

 turicensis, Dinotherium giganteum, Rhinoceros schleiermacheri, Hipparion gracile, 

 Sus erymanthius, Helladotherium duvernoyi, Tragocerus amaltheus, and Gazella 

 brevicornis — are met with in other European deposits assigned to the Miocene 

 period. It is true that one of these deposits at least — that of Eppelsheim — had 

 been shown on stratigraphical grounds to be much more probably Pliocene 

 than Miocene, and the position of other deposits has been determined by the kind 

 of argument which, as I shall show, has proved misleading in the case of Pikermi 

 itself. Nevertheless so general is the consensus of opinion amongst palaeontologists, 

 that the beds with Hipparion at Pikermi and elsewhere are quoted as especially 

 included in the Miocene system by the French Committee of the International 



