4 Prof. Nicholson — Progress in PaJceontology. 



istic fauna of the two deposits. On the other hand, in North 

 America the highest unquestioned Cretaceous beds (the marine de- 

 posits of the Fox-Hills group) are succeeded by a great series of 

 strata, well known as the Fort Union or Great Lignite series, the 

 true stratigraphical position of which has been the subject of much 

 dispute. These deposits consist of nearly four thousand feet of 

 sandstones, shales, and beds of lignite, which rest quite conformably 

 upon the unquestioned Cretaceous deposits of the Fox-Hills group 

 below, and which are succeeded unconformably by unquestioned 

 beds of Tertiary age. In their lower portion they contain a number 

 of marine organic remains, but these gradually disappear as we 

 ascend in the series, and its upper portion is generally characterized 

 by the remains of land and fresh- water shells, associated with a vast 

 abundance of vegetable fossils, chiefly of the nature of detached 

 Dicotyledonous leaves. The difficulty of the problem as to the real 

 age of this great and remarkable deposit arises chiefly from the fact 

 that its marine fossils are fundamentally of Cretaceous type, whQst 

 the remains of plants have an equally distinct Tertiary facies. Thus 

 we find such characteristic Cretaceous Mollusca as Inoceramus, Ammo- 

 nites, Baculites, and unquestionable Dinosaurians [Agailiaumas) side 

 by side with a luxuriant flora of an essentially Tertiary aspect, 

 comprising such modern genera as Quercus, Acer, Pojnilus, TJlmus, 

 Morus, Fagus, Juglans, Alniis, Corylus, Ilex, Platanus, Ficus, Cinna- 

 momum, Smilax, Laurus, Bhamnus, Magnolia, Eucalyptus, TJiui/a, 

 Sequoia, Abies, Taxodium, Sabal, etc. Whilst this association of 

 Cretaceous animals with Tertiary plants is undoubted, much differ- 

 ence of opinion obtains as to how it ought to be interpreted. On the 

 one hand, high authorities, such as Dr. Heer, and Professors 

 Lesquereux and Dana, are of opinion that the plants ought to carry 

 the day, and that the Lignitic Group ought to be considered as the 

 base of the Tertiary series. On the other hand, equally high authori- 

 ties, such as Meek, Hayden, Cope, and Stevenson, are of opinion 

 that the fauna carries more weight than the flora, and that the Fort 

 Union or Lignitic series should be regarded as truly the summit of 

 the Cretaceous. To this view Prof. Newberry, who is in the rare 

 position of having attained almost equal eminence in Palgeozoology 

 and Palasobotany, gives his adhesion, and it is to be considered as in 

 every respect the most probable view, if we take into account the 

 fact that the disputed series is admittedly overlain unconformably by 

 strata of undoubted Tertiary age. Upon the whole, then, when we 

 take into consideration the general unreliability of terrestrial or 

 freshwater mollusca as tests of age, and also the often unsatisfactory 

 nature of stratigraphical conclusions based upon vegetable remains 

 only, I think we can hardly avoid arriving at the opinion that the 

 Great Lignitic series of North America is truly Cretaceous, though 

 probably of a later date than any of the recognized Cretaceous de- 

 posits of the Old World. 



Coming next to the Invertebrates, we find that the last decade has 

 been prolific in discoveries and determinations of great interest and 

 importance, only a very few of which I can notice here, even in the 



