THE JURASSIC AND CRETACEOrf? EPOCn.- 
Grammatophora Mexicana. Spirulina n^iv?}\ 
Navicula Campylodiscus. Biloculina ler ■ 
Navicula cmcigera. Textilaria plicata. 
Siilijnan's American J'jvmal of Science. 
On the Comparative Eootent of Land and Sea during the Jurassic 
and Cretaceous Epochs. Compiled from M. Elie de Beaumont 
and F. S. Beudant, 
In considering the geology of Europe, one of tlie most im- 
portant circumstances which presents itself to our consideration 
is the geology of that district immediately surrounding the 
Thuringerwald — these mountains, of which the Boehmerwald 
is a continuation, form the natural boundaries between Bavaria 
and Saxony and Bohemia. Their range from Cassel to Lintz, 
affords us evidences of the most important disruptions which 
have occurred in the triassic series, and the Jurassic formations 
are disposed on their highly inclined sides in horizontal laj^ers. 
This system exists in other portions, though without offering 
any traces of the same striking phenomena, if we except the 
environs of Avallon and Autun in France. 
This disruption may therefore be considered as having pro- 
duced but little effect on the surface of the globe, although 
doubtless, it constituted one of the most important eras — on 
account of the entire change in organic life, and because the de- 
position of the Jurassic beds, around the more elevated portions 
of the triassic rocks, has recorded their exact boundaries, and 
has thereby enabled us to institute a comparison as to the extent 
of land and sea at this period, and which we have figured in 
Plate I. fig. 2, from the authority of M, Elie de Beaumont. It 
represents the state of Western Europe after the sixth great 
catastrophe to which it w^as subjected, viz. on the upheaval of the 
triassic series. 
The first fact which appears from inspection of the chart is 
VOL. II. NO. XTII. c 
