226 J. W. Judd — On the use of the term Neocomian. 



Dubuisien, &c, — which have been proposed for portions of this 

 formation, and which are not destitute of a local value. ^ 



Two important attempts to dismember the great Neocomian 

 formation have, however, been made since the time of D'Orbigny, 

 and these demand our attention. In 1858 M. Marcou, who has done 

 so much for the elucidation of the structure of the French Jura, 

 argued that the term Neocomian ought to be applied only to the beds 

 originally described by de Montmollin ; and he showed, at the same 

 time, that the palseontological affinities of D'Orbigny's Urgonien and 

 Neocomien etages were so close that they could only be regarded as 

 constituting a single formation. On the other hand, M. Lory's 

 admirable researches in Dauphiny have made known to us the fact 

 that strata, before considered as typical Aptien, are actually inter- 

 stratified with the true Urgonien. In consequence of this discovery, 

 MM. Coquand, Cornuel, and several other distinguished French 

 geologists argue that the Aptien and Urgonien should be joined 

 together to constitue one formation (the Urgo- Aptien), while the 

 beds below (Neocomien of D'Orbigny) should form a second. 



Believing, as we do, with M. Marcou, in the close palseontological 

 affinities of the Urgonien and Neocomien etages of D'Orbigny, and 

 equally, with M. Lory, in the no less close relation of the Aptien 

 and Urgonien, we are led to follow d'Archiac, and to regard the 

 whole of these three divisions as constituting one grand formation. 

 This formation, or system, in places includes nearly 9,000 feet of 

 marine strata, and over wide areas is separated by grand unconformities 

 alike from the Cretaceous above and the Jurassic below. It has an 

 extensive and, in many respects, a peculiar fauna, many of the 

 species of which pass from the bottom to the top of the series, while 

 but very few indeed transgress its limits. The Neocomian does not 

 present closer relations with the true Cretaceous than it does with 

 the Jurassic, with each of which it is in every way worthy to rank 

 as an independent " system." 



The use of the term Neocomian, to include the three etages (Aptien, 

 Urgonien, and Neocomien) of D'Orbigny, which we advocate, is that 

 which is almost universally adopted by the geologists of Switzerland 

 — by MM. Pictet, Eenevier, and others, who have done so much to 

 illustrate the formation and its fauna in their own country. It is to 

 be regretted, however, that these geologists introduce some confusion 

 into their writings by the use, at the same time, of the term Neo- 

 comian proper, for a small portion of the formation (marnes 

 d'Hautcrive). In France the same comprehensiveness is attached to 

 the term as was done by the late M. D'Archiac by a considerable 

 number of geologists, foremost among whom stands M. Hebert, who 

 in several papers has ably defended this extended application of the 

 term. 



For the same system of strata the term Hils has been used in 

 Germany, and the name Biancone in Italy, but both of these are 

 of later date than the name Neocomian. 



' On this subject I would refer the reader to Mr. Davidson's valuable " Notes on 

 Continental Geology," in the Geological Magazine for 1869. 



