THE JURASSIC PERIOD. 71 



the Bristol channel on the southwest to the mouth of the Humber 

 on the northeast. They encircle, with outward dip, the ancient meta- 

 morphic rocks in southern France, and with inward dip they form 

 the border of the Paris basin, the central part of which is filled with 

 younger beds. East of the Paris basin, the upturned beds of the sys- 

 tem appear in the Jura Mountains (whence the name) and the Alps, 

 and farther east in various parts of the complex mountain system 

 of south central Europe. In the lower latitudes of the continent 

 they are to be found in Portugal, in some parts of Italy, in the Balkan 

 peninsula, in the Crimea, and in the Caucasus Mountains, and in the 

 north over large areas in central and northern Russia. The only 

 considerable tract where they do not occur is the northwestern part 

 of the continent. 



This enumeration shows that the Jurassic system is widely dis- 

 tributed in Europe, but as with older systems its present distribution 

 at the surface is no measure of its real extent. It has been thought 

 that the Jurassic of England is probably continuous with that of France 

 beneath the English Channel, and thence, by way of southeastern 

 France, with those parts of the system which appear about the Med- 

 iterranean, and by way of Belgium, the Netherlands, and the Ger- 

 man lowlands, with those parts of the system which appear in Poland 

 and Russia. In northern Russia, the surface distribution of the sys- 

 tem corresponds approximately with its real distribution. In southern 

 Russia, on the other hand, the Jurassic beds are probably widespread 

 beneath younger formations. Jurassic strata of marine origin have 

 a much wider distribution in Europe than in North America, and 

 hence it is inferred that a larger proportion of the former continent 

 was submerged during at least some part of the period. 



It is not to be inferred that all parts of the Jurassic system are 

 so widely distributed. The lower part is less widespread than the 

 Middle, and the Middle is less widespread than the Upper. In this 

 respect, the North American and European continents are in harmony. 



The areas of Jurassic deposition in Europe are commonly grouped 

 into three provinces, the southern, the central, and the eastern; 

 but they are equally well grouped in two provinces, a Mediterranean 

 province and. a Boreal province. 



It is not to be understood that these provinces, whether three or 

 two, were absolutely separated from one another, or that they were 



