234 O. 0. Marsh— Age of the Wealden. 



Art. XXV.— The Age of the Wealden; by O. C. Maesh. 



The Wealden formation of England has long been studied, 

 and is now well known in nearly all its features. Its strati- 

 graphical relations and its Cretaceous age are usually regarded as 

 fully determined, and this is true, also, of the corresponding 

 strata on the Continent. 



The vertebrate fauna of the Wealden is of special interest, 

 and has attracted much attention ever since Mantell in 1825 

 unearthed Iguanodon in the Tilgate Forest. Some of the 

 remains, he sent, through his friend, Professor Silliman, to 

 Yale College, where they have proved of much service. In 

 1865, the writer examined the same famous locality, as well as 

 others on the south coast of England especially rich in verte- 

 brate fossils, and at all of them secured interesting specimens. 

 A study of these in connection with the collections at London 

 and Brussels first made the writer question the Cretaceous age 

 of the Wealden, and a later comparison of its reptilian fauna 

 with allied forms found in the Rocky Mountains led him to 

 the conclusion that both series were Jurassic in type, and 

 should be placed in that division of the geological series. 



At the meeting of the British Association, at Ipswich, in 

 September last, the writer read a paper on European Dinosaurs, 

 including two from the Wealden, and thus the question of 

 their geological age came up for determination. The facts 

 presented by the writer, based mainly upon the reptilian fauna, 

 strongly indicated the Jurassic age of the Wealden, and he 

 urged a re-examination of the question by English geologists.* 

 The subject has since been taken up by Smith Woodward, 

 with special reference to the fossil fishes. In the Geolog- 

 ical Magazine for February, 1896, he gives the main results 

 of his investigation, which prove that the fishes, also, of the 

 Wealden are of Jurassic types, thus placing the geological age 

 of this formation beyond reasonable doubt. The concluding 

 statement of this interesting article is as follows: 



"The Wealden estuary seems to have been the last refuge 

 of the Jurassic marine fish-fauna in this part of the world, not 

 invaded even by stragglers from the dominant race of higher 

 fishes which characterized all the seas of the Cretaceous period. 

 The Wealden river drained a land where a typically Jurassic 

 flora flourished ; the only two known Mammalian teeth from 

 the Wealden resemble those of a Purbeckian genus; and now 

 it is clear that the fishes agree both with these and the reptiles 

 in their alliance with the life of the Jurassic era." 



Tale University, February 22d, 1896. 



* Report, British Association for the Advancement of Science, p. 688, 1895; 

 and this Journal, vol. 1, p. 412, November, 1895. 



