IMPERVIOUS SOIL OF THE OXFORD CLAY. 345 



or greyish, often calcareous and bitu 

 minous beds of the Kimmeridge clay. 



Extent,— The Upper Oolite runs north-east along the northern edge ot 

 the green sand, from the western extremity of Dorset to the extreme north of 

 Norlblk, It is in general only 2 or 3 miles, but in a few places expands to 

 6 or 8 miles in breadth. It appears again on the western edge of tne green 

 sand in Lincolnshire, and in Yorkshire forms a sti-ipe 5 or 6 miles in breadth, 

 which crosses the country from Helmsley to Filey Bay. In the Isle of Port- 

 land also it is found, and it stretches in a narrow stripe along part of the south 

 coast of Dorset. 



Soil. — The soil from tlie Portland rocks, in consequence of the prevalence 

 of siliceous and the absence of clayey matter, produces naturally, or when laid 

 down to grass, only a poor and benty herbage. Its loose and sandy nature 

 makes it also very cheap to work, and hence it is chiefly in arable culture. It 

 is easily affected by drought, but in damp seasons it produces abundant crops 

 — especially in those parts where the soil is naturally mixed with the detritus 

 of the over-lying Hastings sand, and of the calcareous Purbeck beds. 



The Kimmeridge clay forms a tough, greyish, impervious, often however 

 very calcareous soil and subsoil. From the difficulty of working it, much Oi" 

 the surface over which this formation extends is laid down to grass, and the old 

 pasture land afibrds excellent herbage. The celebrated pasture lands of the vale 

 of North "Wilts rests partly on this clay. The relative thicknesses of the Portland 

 beds and the Kimmeridge clay will readily account for the fact of this clay be- 

 ing spread over by far the greatest part of the area occupied by this formation. 

 In Yorkshire, clay of a great thickness is the only member of this series that 

 has hitherto been obsei-ved. On this, as well as on tlie subjacent Oxford clay, 

 the judicious investment of capital might produce a much greater annual breadth 

 of com. 



9°. Middle Oolite. 500 ft. The uppei-most bed in this formation 



Upper Calcareous Grit, ) is a sand-stone containing a consider- 



Coral Rag, > 100. able quantity of lime— next is a coral- 



Calcareous Grit, ) line lime-stone (coral rag) restin;^ upon 



Oxford Clay, ) other sand-stones, which contain much 



Kelloways Rock, > 400, lime in their upper and Httle or none in 



Blue Clay, ) their lower beds. Below these is an 



enormous deposit of adhesive tenacious 

 dark blue clay, frequently calcareous 

 and bituminous, and towards the lower 

 part containing UTCgular beds of sand- 

 stones and lime-stones(Kelloways rock) 

 beneatli which the clay again recurs. 

 Extent. — The middle adjoins the upper oolite on the north and west — ac- 

 companying it from the extremity of Dorset, into Wilts, Oxford, Huntingdon, 

 Lincolnshire, and Yorkshire. Until it reaches Huntingdon, it rarely exceeds 

 6 or 8 miles in width, but in this county and in Lincoln it expands to a width 

 of nearly 20 miles. In Yorkshire it nearly surrounds the upper oolite, and 

 on the northern border of the latter formation attains a width from north to 

 south of 6 or 8 miles. 



Sou.. — The higher beds of both the upper and lower calcareous grits produce 

 good land. They contain lime in termmgled. with the other materials of the 

 siliceous sand-stone. The upper calcareous grits are no doubt improved by 

 their proximity to tlie Kimmeridge clay above them, while the lower calcareous 

 grit is in like manner benefitted by the lime of the super-incumbent coral rag. 

 The under beds of both groups are the more gritty, and form a poor, baxren, 

 almost worthless soil, much of which in Yorkshire is still unreclaimed. 

 Upon the hills of the coral rag itself occurs the best pasture which is met with 



