of the geological record is the fact that between the period of our 
own chalk and the Maestricht beds of Belgium on the one hand, 
and the lower Eocene beds, which in the South of England rest on 
the chalk on the other, there exists a gap which no deposit at 
present known in any part of the world in any satisfactory way 
bridges over.* 
Sir Charles Lyell, comparing the fauna and flora of the Secondary 
and Tertiary deposits, says that the difference between them is as 
great as that between those of the lowest Eocene beds and our own 
times, but it might justly have been said in the present state of our 
knowledge that it is much greater; while Mr. S. Y. Wood, Jun., in 
a little-known paper published in 1862 ,t insisted on the intervention 
of a vast lapse of time between the close of the Secondary and the 
commencement of the Tertiary periods, from the fact of the entire 
extinction during this interval of all the chambered eephalopodous 
molluscs, such as the ammonites, which in Cretaceous times had 
a world-wide range, and of such characteristic and abundant 
Secondary reptiles as the pterodactyles and the ichthyosaurs, and 
other enaliosaurian genera. 
At the close of the Cretaceous period a continent was formed, 
which, in Mr. Wood’s opinion, extended all over the geologically- 
known portion of the globe, and if the evolution theory be true, it 
was upon this post-Cretaceous continent, whose endurance was 
unquestionably so prolonged, that the ancestors of the abundant 
mammalia of the Tertiary period must have dwelt, but of any 
* The thick lignite series of North America has been regarded as 
furnishing a passage between the Cretaceous and the Eocene, but according 
to Professor .Marsh, it forms a well-defined horizon, terminating the Cre- 
taceous series, as it contains the remains of those gigantic reptiles, 
with struthious affinities, called Dinosaurs, so characteristic of the 
Neocomian, or older Cretaceous formations, and of which no trace appears 
in the beds which overlie this series, and rest unconformably upon it ; while 
in these latter, monkeys, carnivorous animals, and those more generalized 
types of the ungulata, from which, as evolutionists maintain, our present 
ungulate orders have descended, make their appearance in abundance. 
t “On the form and distribution of land tracts during the Secondary and 
Tertiary periods.” — Phil. Mag., March, 18G2, p. 1G1. 
