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POPULAR SCIENCE REVIEW. 
covered in the three formations Trias, Lias, and Oolite, and 
some of these are doubtful. This proves how very scanty 
must have been the flower-bearing flora, for we get no similar 
poverty of fossil ferns or conifers. The Wealden formation 
was deposited as a delta at the month of a large river — a river 
watering an enormous area of country, which must have been 
Fig. 1. 
QUBRCUS PRIMORDIALIS, UPPER 
CRETACEOUS BEDS, DAKOTA 
(after Lesquereux). 
Fig. 2. 
BETULA BEATRICIANA, UPPER 
CRETACEOUS BEDS, DAKOTA 
(after Lesquereux). 
more or less covered with plants ; and the Purbeck beds were 
formed along the floor of an extensive fresh-water lake. [No 
conditions could have been more favourable for the preserva- 
tion of land plants than these, yet the number of flowering 
