348 THE CANADIATs' NATURALIST. [Sept. 



lagoons and lakes of the Triassic period Estherict abounded. 

 The varying seas, the estuaries, bays, gulfs, and oceans of the 

 Oolitic period, when land was rising here and sinking there — the 

 sea ever rolling under its tidal laws, and coming and going 

 amongst the ever-shifting land — these seas, we know, swarmed 

 with Entomostraca, amongst the world of marine creatures, and 

 the rivers and lakes were swarming too. The land that bore the 

 great Iguanodon and Megalosaurus — gigantic lizards wandering 

 on tlie marshy grounds, just as the amphibious Hippopotami of 

 to-day wallow along the Airican swamps — had its great rivers ; 

 and their deltas like those of the Ganges and Mississippi, con- 

 sijited of mud-banks and muddy lagoons full of Uniones, Palu- 

 dime, Ci/rence, and other shell-fish, and above all, with Cypridce 

 and Estherice, feeding on the dead molluscs and fish. 



The Sussex marble is mainly composed of these sometimes ; 

 some beds of freestone at Swanage are wholly made up of them, 

 and flake after flake of black clay, once mud, may easily be 

 picked by the hand, in the Isle of Wight, in cliifs some miles in 

 extent, from beds of shale nearly two hundred feet thick, every 

 surface being thickly coated with the shells or carapaces of these 

 minute creatures. What durable witnesses of a long-past age ! 



The "Age of Reptiles" passed away, the land and its rivers 

 went down, the sea-bed and the estuaries were coated over with 

 new sands and clays, derived from new clifi"s and new lands, 

 washed by the untiring, enduring sea. Some parts of what is 

 now the European area sank several hundred feet, and was 

 covered by a deep sea, and in this were formed successively the 

 Greeusand, Gault and Chalk. The shores were thus gradually 

 changed, and the new land elsewhere raised up, or remaining as 

 islands here and there, bore new plants, new trees, and new 

 animals ; the sea also brought forth new Entomostraca, which 

 may be easily obtained by washing the Gault clay into nmd, 

 drying and sifting it, and by washing the Chalk into powder, and 

 examining it with a glass.* 



Another great change occurred over half the world, at least ; 

 the strata that had been accumulating in gradually deepening 

 seas, and on sinking sea-beds, were hoisted up again by subter- 

 ranean force, and a new era was inaugurated — recognized by 

 geologists in the sands, clays, and limestones which they denomi- 



* See some notes on the preparation of clajs, sauds, and chalk, for 

 microscopical purposes, in the " Geologist " 8ir)S, vol. i., p. 249. 



