462 THE JURASSIC PERIOD 



Jurassic Life 



The life of the Jurassic has been preserved in wonderful fulness 

 and variety; but with comparatively few exceptions, our knowledge 

 of it has been principally derived from Europe, where a host of 

 eminent geologists have long studied the great wealth of material. 

 The contrast between North America and Europe in regard to the 

 relative abundance of Jurassic marine fossils is seen from the fact 

 that while in Great Britain alone more than 4000 species have 

 been described, in America hardly one-tenth of that number has 

 so far been found. 



Plants. — The flora of the Jurassic differs little, on the whole, 

 from that of the Trias, and is made up of Ferns, Horsetails, 

 Cycads, and Conifers. Tree ferns flourished in northern Europe 

 in great variety. The Cycads attain their culmination of abundance 

 and diversity in this period, no less than forty species occurring 

 in a single horizon of the English Upper Jura ; some of them, like 

 Paheozamia, have leaves exceeding one foot in length. The Coni- 

 fers are of somewhat more modern aspect than those of the Trias, 

 and, from their resemblance to genera which are still extant, have 

 received such names as Thujites, Taxites, Cupressites, Pinites, etc. 

 The Araucarian pines still flourished in Europe. Monocotyledons 

 have been reported from the Jurassic, but the evidence for their 

 existence is very doubtful. 



Foraminifera are found in great numbers and variety in the soft 

 Jurassic clays, many of them belonging to genera which still 

 abound in the modern seas. It must not be supposed that these 

 organisms first became so abundant in Jurassic times ; it is merely 

 that the conditions for the preservation of these microscopic and 

 exquisite shells had not been so favourable before. 



Radiolaria. — The beautiful siliceous tests of the Radiolarians 

 are also found in multitudes. In the Alps occur whole strata of 

 red flints and jaspery slates, which are composed almost entirely 

 of these tests. 



Spongida. — Sponges are found in wonderful profusion and 

 diversity and in such perfect preservation that every detail of their 



