THE ME SO ZOIC ERA

Auckland Star, Volume LXVII, Issue 253, 24 October 1936, Page 6 (Supplement)

THE ME SO ZOIC ERA

By J.M.D. (Christchurch)

XTJIZ now leave the Palaeozoic era yy and tui;n to the next on the table, the Mesozoie. This is the most interesting of all the time divisions, and we are going to spend quite a lot of time studying it. You will see, on the geological time-table, that there are three periods in the Hesozoic —the Triassic, the Jurassic and the Cretaceous, and the era is of about 140,000,000 years' duration. As our study of this era is going to take us into all parts of earth, I suggest we make a summary of the geological history of the most important countries. Now look at the map (of the week before last) of the Permian world. The major incidents of the Mesozoic era are (1) the gradual break-up of the great continent Gondwanaland; (2) the connection, across Russia, of Atlantis with Asia in Triassic 'times and the break through again by the sea of Tethys in the Jurassic; and (3) lastly the.southward extension of Tethys to separate South America from Africa. This extension is explained by one school of geologists ■as due to tie foundering of a land connection between the two continents, while the second school holds "that the two continents drifted apart. Similarly this latter school believes that Gondwanaland broke up by the drifting apart of large sections of it, while the former school believes that huge areas of it sank beneath the sea, leaving Africa, India, Australia, Antarctica and South America, as remnants. Now' for the more detailed history:— Europe.—Two types of rock occur, 'continental' and oceanic. In Ger-; many, the type area, three stages in the Triassic occurred. The earliest "rocks prove that Germany was a high-lying, arid country, with sandy deserts and oases. Then came an incursion of the sea, covering Germany and causing deposition of sediments. Lastly, there was uplift and the connection with the sea was cut off. The salt lake then evaporated, leaving great thicknesses of salt which are being mined to-day at Stassfurt. In the lower Jurassic most of the land was above water, and many fresh-water, lakes left their deposits. In the upper Jurassic the greatest transgression of the sea in geologicalhistory occurred when,

Tethys flooded Europe and most of Asia. By lower Cretaceous times much-of the sea had retreated, leaving large inland seas and lakes. One of these deposited the Wealden limestone, and it is to this bed that the Anglo-Iranian Oil Company is drilling in the hopes of finding oil in

Britain. In the middle. Cretaceous subsidence of the land had caused most of Europe to become a gulf, ■with Belgium as an island. In the upper Cretaceous Europe was elevated once more, and Tethys had greatly shrunk to approximately what is now the Mediterranean. North America.—For the most part this continent was above water. In the Triassic the continent Atlantis extended eastwards to join Eurasia. Western America was flooded, and in

the east continental deposits were laid down while activity broke out, lava being interbedded with land shingle. In .Jurassic times an arm of the North Pacific (Boreal Sea) stretched from Alaska down through mid-western United States, depositing the sediments which were to form the Rocky Mountains, Cascades and Sierras. This arm of the Boreal Sea, with its northern forms of life, reached to Mexico, where it was separated from a westward arm of Tetliys, with its European life, by a very narrow isthmus. The lower Cretaceous saw the withdrawal of much of the Boreal extension and a

irorthward transgression of the Mexican eea to Wyoming. Then in the upper Cretaceous the seas once more transgressed, the Boreal arm stretching southwards again and an eastern sea, from the Great Lakes to the Gulf of Mexico, dividing Eastern from Western America. The era was brought to a close by great uplift which formed the Rocky Mountains (later reformed by the Alpine Revolution) and left America above the sea for all Tertiary time.