DRlFr NEAR THE CITT OF DURHAM. 271 



pounds to many tons in weight. These are generally dug up when they 

 obstruct the plough, and are sold for mending the roads at about 5s. a 

 ton. This clay varies in depth, from one or two, to fifty or sixty feet. 



2°. Beneath the clay occurs an accumulation of fine, generally yel- 

 low, more rarely red, sand, intermixed with occasional layers and 

 round hills of gravel — with frequent black streaks of rounded coal dust, 

 and here and there with nests of rounded lumps of coal, from half an 

 inch to fiv%or six inches in diameter. This coal is sometimes so abun- 

 dant as to be collected and sold for burning. 



The gravels, where they overlie the coal measures, consist chiefly of 

 rounded, and on the upper part occasionally of large angular masses 

 of coal sand-stones — with here and there a fragment of trap, of 

 mountain lime-stone, or of some of the older rocks to be met with in 

 the mountainous districts towards the west. Over the magnesian lime- 

 stone, however, in -the south-eastern division of the county, towards the 

 foot of the south-eastern slope of the magnesian lime-stone hills, the gra- 

 vels which exhibit in some places (Wynyard) an irregular stratification, 

 contain many rounded masses of magnesian lime-stone, and even of 

 new-red sand-stone — the evident debris of adjacent rodis long'ago bro- 

 ken up. 



3°. Tlie undermost layer which rests immediately upon the subjacer 

 rocks consists of a stiff unstratified blue clay often full of trap boulders 

 but containing also occasional large rounded masses of blue lime-stone 

 — and smaller pebbles of quartz, of granite, and of the older slate rocks. 

 In many localities this clay is wanting, and the sands or gravels rest im- 

 mediately upon the carboniferous or magnesian lime-stone rocks — while 

 m some tracts, both this and the upper clay appear to degenerate into a 

 stony most unmanageable clayey gravel. I am not aware that the 

 large whin (trap) boulders are ever met with in the beds of sand. 



The following diagram exhibits the mode in which these drifted mate- 

 rials present themselves in the neighbourhood of the city of Durham. 

 The cross (I) indicates very nearly the site of Durham on the banks of 

 the river Wear. 



No. 1 represents the coal measures. 



2. The lower new-red sand-stone, here soft and pale yellow. 



3. The magnesian lime-stone rising into a high escarpment from 3 to 

 6 miles south of the city. 



4. Yellow loose sand — with rolled sand-stones and coal-drift — occa- 

 sionally stratified. It forms the numerous picturesque round hills in the 

 neighbourhood of the city, and varies from a few feet to not less than 120 

 feet in thickness. 



5 is the upper clay, with boulders. N indicates Framwellgate 

 Moor, where it is only a few feet thick. At S, on the southern slope of 

 the escarpment, it some'imes rests immediately on the rock as here re- 



