GEOGRAPHICAL DISTRIBUTION OF THE FLORA. 33 
The mode of accumulation of the beds at Aachen seems to have been 
similar to that of the Amboy Clays and the Potomae group; that is, they 
are local estuarine beds resting upon Paleozoic rocks and composed of the 
wash of the neighboring land, in which were buried great numbers of leaves 
and trunks of the trees which grew upon that land. The trunks are now 
converted into lignite, and they are as conspicuous an element in the lithol- 
ogy of the group as in New Jersey. Dr. Debey supposed that his collection 
contained 300 to 400 species of angiosperm plants. This is perhaps an 
exaggeration, for he included in his list a great many doubtful fragments; 
but when the floras of the Aachen beds and those of the clays of New 
Jersey shall be fully studied and illustrated it will undoubtedly be found 
that the botanical aspects are the same, and that there are perhaps as many 
species identical in the two formations as in those of Greenland and New 
Jersey. Hence, we may fairly infer that the collections of plants from the 
New Jersey clays, the Dakota group, the Patoot and Atane beds of Green- 
land, the Aachen series of Germany, and the plant-bearing Cretaceous rocks 
of Bohemia fairly represent the vegetation of the world during the middle 
and latter portions of the Cretaceous age. 
MON XXvI——3 
