74 



GEOLOGY. 



the larger part of the Middle Jura is wanting, though the upper horizons 

 may be present. Middle Jurassic beds in Lat. 71° have yielded species 

 of sub-tropical ferns, cycads, and conifers. 1 



The Upper Jura. — The encroachment of the sea which was in progress 

 during the Middle Jurassic time reached its maximum a little later 



Fig. 355. — Sketch-map of Europe in the Middle Jurassic period. The shaded areas: 

 are areas of deposition, chiefly marine. (After De Lapparent.) 



as shown by the wide distribution of the Upper Jurassic formations; 

 but before the end of the epoch the sea began to withdraw, for some 

 parts of the area which had been submerged became land, while other 

 parts were occupied by lakes and bodies of brackish water. 



The formations of the Upper Jurassic in central Europe contain 

 much more limestone than those of the lower divisions of the system 

 in the same province. Corals and sponges were especially abundant 

 in central Europe, and contributed much to the' making of the light- 

 colored limestone which, on the continent, has given this member 



De Lapparent, Traite de Geologie, p. 1142. 



