January 22, 1897.] 



SGIENGE. 



15i 



eousana, Natica Alhleta, Trigonia Barrensis, Tri- 

 gonia Boloniensis, Mytilus portlandicus, Mytilus 

 Tombecki; and finally the Hemicidaris Purbeck- 

 ensis of Forbes. The second group at the very 

 top of the Jurassic formation, called in Franche- 

 Comte ' Dolomies portlandiennes ' of Marcou 

 (Etudes geologiques sur la Franche-Comte septen- 

 trional, Le sysieine ooliiique, par Albert Girardot, 

 p. 369, Paris, 1896), contains also a special 

 fauna, indicating at some places a brackish for- 

 mation, such as : Corbula, Anisocardia, Cyrena, 

 Frotocardia, Lucina, Corbicella and Gervilliana. 

 However, at Gray (Haute Saone) the fauna is 

 entirely marine, and Prof Etallon, who has 

 given a detailed description of that portion of 

 Franche-Comte, has called it ' Diceras Port- 

 landian beds.' In both divisions, or groups, 

 corals are common round Gray, Morteau, Pon- 

 tarlier and Salins. The thickness of the two 

 groups varies between 150 and 600 feet, accord- 

 ing to the more or less denudation of the upper 

 portion of the strata. 



Prof Albert Oppel, of Munich, had created, 

 in 1865, his Tithonic, or Tithonian formation 

 (Die Tithonische Eto.ge, Zeitschr. deutschen geo- 

 logischen Gessellschaft, Jahrg, 1865, pp. 535- 

 558, Berlin) to designate a special form of the 

 divisions of the upper Jura, such as the Pur- 

 beck strata, the Solenhofer Schiefer and the 

 Portland kalk, of the Alpine area and of the 

 Mediterranean basin ; it was a happy name, 

 meaning that the groups of beds containing 

 paleontological precursor forms of the Creta- 

 ceous fauna can be considered as a forerunner 

 formation, announcing the arrival of another 

 great system. Many papers have been pub- 

 lished since the premature death of Oppel, in 

 November, 1865, on that important question, 

 the most remarkable being by Colonel A. Tou- 

 cas, entitled 'Elude de lafaune des couches titho- 

 niquesde V Ardeche' (Bull. Soc. Geol. France, 3d 

 series. Vol. XVIII., pp. 560-629, Paris, 1890), 

 in which he showed the existence of three dif- 

 ferent faunas, called Lower Tithonic or Diphy- 

 akalk, Middle Tithonic or Ardescian, and 

 Upper Tithonic or Berriasian-Puberkian. 



In England nothing can be correlated 

 with those six hundred feet of limestone de- 

 posited in the Jurassic sea of southeastern 

 France, of the Swiss Alps, of the Tyrol, of 



Stramberg (Carpathes), of Andalusia (Spain), 

 but the brackish and fresh-water deposits of the 

 Wealden formation. At Speeton there is noth- 

 ing like it. The Portland stone is lacking 

 there, very likely destroyed by denudation, 

 and the series of Speeton clay is decidedly Neo- 

 comian,'as it has been amply proved by Messrs. 

 Judd, Lamplugh and Pavlow. If we consult 

 the geological map of England, we see that 

 directly over the small Portland beds, only eight 

 or ten feet thick, we have brackish and fresh- 

 water deposits, at first containing a few marine 

 beds with the Hemicidaris Purbeckensis of 

 Forbes, then becoming exclusively fluviatile, ex- 

 tending southward of Dorsetshire and the Isle 

 of Wight, turning northward in the English 

 Channel, reaching again the terra firma at Hast- 

 ings and its environs, covering in the form of a 

 cut ellipse all the country of the Weald, be- 

 tween the North Downs and South Downs 

 (Kent and Sussex counties). We have there a 

 sort of gigantic fossil mound, the remnant of a 

 great delta or estuary deposit, like those actually 

 going on at the mouth of the Ganges or of the 

 Amazon. Farther west than the Weald region 

 that formation lies directly over the Portland 

 stone in the vale of Wardour, and very likely 

 it extended northward. At the end of the Jura 

 epoch the dislocation which has emerged the 

 Jura formation in England and on the conti- 

 nent of Europe put a stop to those fresh-water 

 deposits, and, being emerged as dry land, denu- 

 dation began to remove easily such loose mate- 

 rials as clay and sands, leaving only the large 

 semi-elliptical patches of southeastern England. 

 The denudation lasted as long as the Neo- 

 comian or Lower Cretaceous deposits were going 

 on at Speeton and in France and Switzerland ; 

 then by a general subsidence, affecting the whole 

 coast of eastern England, the sea of the York- 

 shire coast invaded the whole country south, 

 depositing on the beds of the Wealden forma- 

 tion, and in some parts over the beds of the 

 Portland stone and Kimmeridge clay, the strata 

 called Lower Green Sand, Gault, Upper Green 

 Sand and Chalk. The proof that the green 

 sand sea came after the denudation, and even 

 complete removal in some places of the Weal- 

 den, is shown by the existence of Lower Green 

 Sand west of Hastings, lying directly on the 



