South-west and North of France, and South of Germany. 141 
Qdly, The magnesian J ura cavernous mass ; 3 dly, The com- 
pact and oolitic part ; 4 tidy. The schistose lithographic part, 
which is so rich in fishes and crabs ; bthly. The clay marl with 
globular iron-ore. 
The magnesian Jura limestone presents most singular varie- 
ties. When it is a congeries of triturated marine bodies, as near 
Ratisbon, it assumes the appearance of the porous yellow 
limestone of the Leithagebirge near Vienna in Austria. The 
petrifactions or fossils of the compact limestone are very abun- 
dant. I would recommend to collectors to go to Amberg, 
which is one of the best places, and where Professor Graf, a 
gentleman of erudition, and who has travelled much, sells for a 
trifle all the petrifactions of the neighbourhood. 
Chalk is only deposited upon the J ura limestone near Ratis- 
bone, yet the ferruginous marl connects already the two forma- 
tions ; the green sand, and the chloride chalk with Gryphites, 
columba Brg. and spirata Schlottheim, form the chief parts of 
this deposit. A yellowish-brown limestone, with some madre- 
pores, seems to belong also to it ; and under the green sand is a 
coarse quartzose and calcareous conglomerate, and some nests 
of a good refractory clay (Abach). 
In the basin between the Bohmerwaldgebirge and the Black 
Forest, there are no tertiary deposits, and only fluviatile marls 
with land shells, and some calcareous tuffa with bones of quad- 
rupeds ; yet, in the J ura chain, there exist at Ulm, at Stein- 
heim, and in a great basin near Wallersten, Oettingen, Nordlin- 
gen, &c., fresh-water limestone deposits, with the common shells 
of the genera Lymnsea, Planorbis, Helix, and Paludina. At 
Steinheim, the deposit is, in its lower part, sandy, and so full 
of shells that one may collect them in bushels. Basaltic erup- 
tions have, here and there, found means to traverse the Jura 
chain : they are chiefly tuffa, full of altered pieces of Jura lime- 
stone (Urach, Gottingen) ; they form large veins or columns, 
and, in some instances, present themselves in the form of veins 
of basalt, as near Doneschingen. In the Hegau, they form 
cones of clinkstone ; and on the base of the Fichtelgebirge cones 
or columns of basalt, sometimes with balls of olivine and pieces 
of granitose porphyritie rocks, reduced to the state of basalt 
