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the Chalk Period which closes the long and exuberant 

 life of the Mesozoio Series. It is in this Period that 

 the strata left by the receding Ocean are mostly com- 

 posed of Chalk, hence the name. We meet the great 

 Iguanodon (the great land Saurian) larger than the 

 Megalosaurus of the preceding Era — the Reptiles of 

 the two preceding Eras belonged more to the Croco- 

 dile type, but now they belong more to the Lizard 

 (Saurian) ; they no more crawl, but are borne on paws. 

 The Flora of this Era seems more to be the continua- 

 tion of the last, — seaweeds, Irish- moss, fei'ns, coni- 

 fers, cycads are the chief types of Cretaceous vegetation. 

 The Marine Fauna abounds in foraminiferous orga- 

 nisms which by the continuous dropping of their 

 calcareous substances form such a thick layer of Chalk 

 that more than the half of the strata of chalk is com- 

 posed of their deposits (exuvi^). 



The Ichthyosaurus, and the Plesiosaurus of the 

 preceding Eras make way for the Mosasaurus, the Sea- 

 Lizard, which forms the subject of this Paper, a Fossil 

 of which was recently found in a quarry near Mons . 

 it is so called being particular to that part of Belgium 

 watered by the "Mouse," comprising chiefly the three 

 Central and the three Southern Provinces of Belgium. 

 The first Fossil of this Gigantic Reptile was found in 

 the sandy yellow Limestone of Maestricht (Limbourg) 

 known as the Danian Strata, in 1764 or 1765, by some 

 workmen employed in a quarry of building-stone, 

 which quarry extends from Maestricht to Liege. It 



