480 MESOZOIC TIME — REPTILIAN AGE. 



(4) other limestones, either loose or compact. Among the sandy 

 portions the Green-sand beds are a marked feature, especially of 

 the lower part of the formation. This is so eminently the fact 

 that the Lower Cretaceous in England is called the Green-sand, 

 although only a part of the layers are green, and in some regions 

 none at all. 



The Chalk often contains flint in nodules, which are distributed 

 in layers through it like the hornstone in the earlier limestones. 

 They are more or less rounded, and often assume fantastic shapes. 

 Sometimes they resemble rolled stones ; but in fact all are of con- 

 cretionary origin. The exterior of the nodules for a little depth 

 is frequently white, and penetrated by chalk, proving that they are 

 not introduced boulders or stones, but have originated where they 

 lie. Moreover, many chalk fossils are turned into flint, and it is 

 common to find a mass of flint with a fossil as its nucleus. 



The Cretaceous beds of Europe have been divided into — 



1. The Lower Cretaceous, including in England the Lower Green-sand, 800 

 to 900 feet thick, and in other regions beds of clay, and limestone sometimes 

 chalky. 



2. The Middle Cretaceous, including in England (a) the clayey beds or marls 

 called Gault, 150 feet thick, and {b) the Upper Green-sand, 100 feet. 



3. The Upper Cretaceous, including in England the beds of Chalk, in all about 

 1200 feet: it consists of (a) the Lower or Gray Chalk, or Chalk Marl, without 

 flint; (6) the White Chalk, containing flint; (c) the Maestricht beds, rough friable 

 limestone at Maestricht in Denmark, 100 feet thick. 



The subdivisions of the Cretaceous are variously named in different parts of 

 Europe. 



Lower Cretaceous. — Superior Neocomian of D'Orbigny (the Wealden being 

 the inferior) ; also his Aptian ; the Hils-conglomerat of Germany. 



Middle Cretaceous. — 1. Gault, Albian of D'Orbigny, Lower Pl'anerkalk of 

 Saxony. — 2. Upper Green-sand, Cenomanian of D'Orbigny, Lower Quadersand- 

 stein of the Germans. 



Upper Cretaceous. — 1. Gray Chalk, or Chalk without flints, Turonian of 

 D'Orbigny, Hippurite Limestone of the Pyrenees, Upper Planerkalk of Saxony. 

 2. White Chalk, or Chalk with flints, Senonian of D'Orbigny, Upper Quader- 

 sandstein? of the Germans, La Scaglia of the Italians. 3. Maestricht beds, 

 Danian of D'Orbigny, Calcaire pisolitique near Paris. 



In North America the Earlier Cretaceous corresponds, according to Meek & 

 Hayden, to the inferior division of the Upper Cretaceous of Europe, or the Gray 

 Chalk, with perhaps part or all of the Middle Cretaceous; and the Later Creta- 

 ceous, to the superior division of the Upper Cretaceous, or the White Chalk. 



In mineral character the beds of each division vary much over Europe, the 

 Chalk of England being synchronous with marls and solid limestones in Europe. 



The Cretaceous of Great Britain is not found on any part of the Atlantic 

 coast, excepting a small area in the vicinity of the Giants' Causeway. The beds 

 of northern France spread eastward over Belgium and Westphalia, but not to 



