104 PROCEEDINGS OE THE GEOLOGICAL SOCIEir. [Jan. 8, 



The marine strata associated with the various groups of estuarine 

 beds in the Scotch Jurassic system also exhibit many very interest- 

 ing characters. As compared with their equivalents in England, 

 they usually show indications of having been of more shallow- water 

 origin, and accumulated under conditions of a much more local cha- 

 racter. "While on the one hand there is a general absence of the 

 thick masses of clays, formed of fine sediment and crowded with 

 pelagic forms of life, like large portions of the Lias, and the Oxford 

 and Kimmeridge clays, we find in many parts of the series great 

 accumulations of conglomerate made up of the local rocks. At the 

 same time there are not wanting proofs that, during certain por- 

 tions of the Jurassic period, marine conditions prevailed over a veiy 

 considerable area; and it is in these that the strata are found 

 to assume the comparatively deeper-water and more normal cha- 

 racters. 



The remarkable feature of the frequent recurrence of estuarine 

 strata, though characteristic of the Scottish Jurassic series, is not 

 peculiar to it. In the southern province of Sweden (Scania) we find 

 a precisely similar set of phenomena to those which we have been 

 noticing as so strikingly displayed in Scotland. 



In Sweden the Secondary strata are exposed under the same dis- 

 advantageous conditions as in Scotland. Almost everywhere the 

 surface of the country is concealed by great masses of drift of various 

 kinds, above which a few hard ridges of Mesozoic rocks rise in iso- 

 lated patches. Some of these patches are composed of Chalk and 

 Upper Greensancl; others of Jurassic strata presenting very peculiar 

 characters. The exact geological relations of these singular frag- 

 ments of Secondary strata have not apparently been fully deter- 

 mined, but, like the similar beds of Scotland, they are developed in 

 the immediate vicinity of great masses of Silurian and granitic rocks. 

 The Jurassic strata of Sweden consist of alternations of sandstones, 

 shales, grits, quartzose conglomerates, impure lignites, and workable 

 seams of coal : in some places these beds yield a beautiful flora ; in 

 others they contain bands with marine shells. These strata have 

 been studied by "Wahlenberg, Nilsson, Hisinger, Murchison, Braun, 

 and others : and by some authors, as Brongniart and Mantell, they 

 have been regarded (as were the estuarine Jurassic beds of Scotland) 

 as representing the Wealden. 



The two most important patches of these strata, those of Hogonas 

 and Hor, have lately been made the object of careful and exact study 

 by M. Hebert, who has shown that the marine strata at the base of 

 the former contain a fauna which enables us to assign them to the 

 base of the Lower Lias, while the evidence with regard to the latter, 

 though less decisive, is such as to lead us to consider them to be of 

 nearly the same age *. 



Thus we see that there are reasons for believing that over a vast 

 area, comprising the northern limits of the Anglo -Parisian basin, a 



* " Reckerclies sur l'age des gres combustibles d'Helsingbord et d'Hogonas 

 (Suede meridionale), par M. Hebert," Annales des Sciences geologiques, tom. i. 

 p. 117; Bull, de la Soc. Geol. de France, 2 e serie, tom. xxvi. (1870) p. 366. 



