CHAP. IX.] JURASSIC PERIOD. 139 



field Beds, and contain the remains of many plants and 

 terrestrial animals. 



In the continuation of the series to the north-east these 

 estuarine beds thicken at the expense of the Great Oolite 

 limestones, while other beds of a similar character replace 

 part of the Inferior Oolite. Moreover, in Northampton, 

 the two estuarine groups are separated by a plane of 

 erosion or unconformity, and the whole series is in some 

 places reduced to less than 100 feet, of which only 30 feet 

 are marine limestones. 



In Lincolnshire there is a greater thickness of marine 

 limestones, a lenticular mass of limestone coming in 

 between the two estuarine groups, but this becomes very 

 thin in the north of that county, and in Yorkshire the 

 estuarine beds thicken, so that they eventually form a thick 

 series of deposits in which marine limestones are quite 

 subordinate features. As this Yorkshire series is such a 

 contrast to that of the south-western counties, a brief 

 account of its component members may be given. 



At the base of the section are marine sandstones and 

 ironstones (about 50 feet thick). Above these is a group 

 of estuarine sandstones and shales, with much carbona- 

 ceous matter and thin seams of impure coal ; this group is 

 280 feet thick near Whitby, but thinner to the westward. 

 Then comes a band of calcareous sandstone, which contains 

 marine fossils, and appears to be the attenuated represen- 

 tative of the Lincolnshire Limestone; but above this is 

 another mass of estuarine deposits, from 50 to 100 feet 

 thick, containing several workable seams of coal. This 

 group is succeeded by the Scarborough Limestone, a len- 

 ticular mass, which is thin on the coast, but thickens to the 

 west and north-west. Above this limestone is a third set 

 of estuarine shales and sandstones, from 120 to 220 feet 

 thick, which are generally supposed to represent the Great 

 Oolite, as they are covered by the Cornbrash, and there is 



