586 



SCIENTIFIC RECREATIONS. 



of enormous size. Nor were insects absent. Numbers of remains have 

 been discovered ; beetles, dragon-flies, grasshoppers, etc., in multitudes yield 

 us information, while the marine fossils, star-fish, mollusca, and various 



Fig. 673. Pterodactylus longirostris. 



fishes, are of frequent occurrence. Animal and vegetable life during this 

 period must have been very rich and varied literally leaving " footprints in 

 the sands of time." 



The " Blue Lias " is a term familiar to every reader. It is a kind of 

 limestone mixed with clay, of a blue colour, and upon this we find the 

 Oolitic, or Oolite System so called because it somewhat resembles the roe 

 of a fish. The Lias clays are used for bricks, and Whitby "jet" is also 

 obtained from the Upper Lias. Jet is really a lignite, or wood in the 

 process of transmutation. In this Lias formation, besides the numerous 

 fossil remains already mentioned, we find the " snakestones" (ammonites), 

 the stone-lily, and belemnites, with many nautili and shells. 



The OOLITE, or JURASSIC, underlies the chalk, and overlies the Trias 

 formation. The term "Jurassic" originates from the Jura range, which is 



Fig. 674. Ichthyosaurus. 



almost entirely composed of Oolitic strata. These strata are greatly dis- 

 torted by pressure, and when we reach Switzerland and the familiar Alps, 

 we find gneiss, crystalline, limestones, and schists, into which the Oolite has 



