186 MIDDLE AND UPPER OOLITE PORTLAND OOLITE. 



This imperfect coal formation appears to be entirely wanting in 

 England south of the Humber. In Savoy, I examined a coal for- 

 mation which is placed between two beds of limestone and over lias : 

 this I believe to be analogous in position, to that in the eastern moor- 

 lands of Yorkshire.'^ 



Between the lower and the middle oolites occurs a bed of dark 

 blue clay called Oxford or clunch clay ; the thickness has been esti- 

 mated at two hundred feet. Some of the beds are bituminous, and 

 bear a near resemblance to lias clay ; they abound in Septaria : oth- 

 er beds are much intermixed with calcareous earth. In the lower 

 part of the Oxford clay, irregular beds of limestone occur, which 

 have received the name of Kelloway rock, from being found near 

 Kelloway bridge, in Wiltshire. The bones of one species of icthy- 

 osaurus, different from those in the lias, have been found in the Ox- 

 ford clay. 



The MIDDLE DIVISION of ooUie consists, 1st, Of beds of siliceous 

 and calcareous sandstone. 2d, Coralline limestone beds, containing 

 numerous madrepores, in some parts called coral ragg. 3d, Oolite, 

 sometimes called Oxford oolite, which agrees in many of its charac- 

 ters with the Bath oolite, in the lower division. The beds of the 

 middle oolite pass into each other, and may be regarded as one for- 

 mation. They vary much in their thickness and succession in differ- 

 ent districts. The average thickness of the whole, has been estima- 

 ted at two hundred feet. 



Between the Middle and the upper Division of oolites, there oc- 

 curs, in the western counties of England and on the coast of France, 

 near Boulogne, another thick bed of clay, which has received the 

 name of Kimmeridge clay.f It is a greyish clay passing into the 

 state of shale, and is sometimes so bituminous as to be used for fuel : 

 its thickness in some parts is more than one hundred feet. Bones of 

 saurian or lizard-shaped animals have been found in this clay. 



The UPPER DIVISION of oolite comprises the beds of Portland 

 stone, which have been well described as a calcareo-siliceous free- 

 stone, with beds and nodules of flint. In the Isle of Portland, where 

 - the middle bed of the Portland stone is quarried for architectural pur- 

 poses, it is covered by a cream-coloured stone called cap, which is 

 only burned for lime : under this, there are two beds of workable 

 stone, each five feet thick, separated by grey flint, and a third bed of 

 the best stone below. The total thickness of the three beds of build- 

 ing-stone varies from 17 to 24 feet. The Portland series, which 

 forms the upper termination of the English oolites, is neither of great 

 extent (being confined to the county of Dorsetshire), nor of con- 

 siderable thickness. It is succeeded by beds of limestone, called the 



* Travels in the Tarentaise. 



+ From Kimmeridge in Dorsetshire, where the bituminous shale is called Kim- 

 meridge coal. 



