268 The Realm of Nature CHAP. 



348. Newer Primary Rocks. In the Permian period, 

 named after the Russian government of Perm, where the 

 rocks of this age are greatly developed, plant life appears 

 to have been less abundant and varied than in Carboniferous 

 times, but remains of great amphibians abound, and those of 

 true reptiles appear for the first time. Palaeozoic rocks some- 

 times exert a considerable local influence on a freely sus- 

 pended magnet ( 98). In the course of a magnetic survey 

 of the British Islands, Professors Thorpe and Riicker recently 

 found a line of magnetic disturbance running across the 

 comparatively recent strata of southern England, coincident 

 with a deeply buried mass of Palaeozoic formation running 

 from the old mountains of Wales toward the Carboniferous 

 region of the continent of Europe, the existence of which 

 had previously been inferred from geological evidence. 1 In 

 1890 this conclusion was strikingly confirmed by the dis- 

 covery of coal in a very deep boring through the tertiary 

 rocks of eastern Kent. 



349- Secondary Rocks. The secondary rocks are 

 termed Mesozoic, because they contain evidence of the 

 existence of living creatures intermediate between those of 

 the Primary period and of the present time. In the Trias 

 there are signs of gigantic amphibians, reptiles of the croco- 

 dile kind, and of the simplest forms of mammals, the mar- 

 supials. The Jurassic system takes its name from the Jura 

 Mountains, and is sometimes known as Oolitic (egg-stone), 

 from the granular limestones resembling the structure of a 

 fish-roe, by which it is characterised. Many beds of lime- 

 stone of this period are fossil coral-reefs. The most abun- 

 dant mollusca were the ammonites, with wonderful rolled 

 shells, and cuttle-fishes. Saurians reptile-like animals 

 grew in those days to an enormous size, and inhabited air, 

 sea, and land. The Pterodactyls were small reptiles with 

 wings not unlike those of a bat in appearance. Ichthyo- 

 saurus and Plesiosaurus were swimming reptiles, some- 

 times 40 feet in length, and the land reptiles were probably 

 the hugest animals that ever inhabited the globe the 

 remains of the Atlantosaurus, discovered in North America, 

 indicating a length of 100 feet and a height of 30 feet. 



