86 Ohervations on the Geologij 



light on the globular and columnar structure common to many 

 rock formations. 



Nearer to Sunderland, below the garden of the rectory, there 

 is another remarkable quarry. If the limestone here once ex- 

 isted in continuous beds, it has been subsequently broken and 

 throu-n into the utmost confusion ; large shapeless masses being 

 piled together, and the intermediate spaces filled with calcareous 

 sand similar to that before mentioned at Fulwell. 



The limestone of this district, though abounding in magnesia, 

 is sent in prodigious quantities to Scotland for agricultural use ; 

 which offei-s a farther confirmation of what I have stated before 

 in my Introduction to Geology, that magnesian limestone, so 

 •far from behig prejudicial to land, is preferable to any other 

 tvhere it is to be sent to a distance ; for the same quantity will 

 produce an equal effect to a larger quantity of the common 

 khid*. 



The coal district of Northumberland and Durham is bounded 

 by the magnesian limestone, or by the sea, on the east, and by 

 the metalliferous limestone on the west. Dr. Thomson has di- 

 vided this district into two formations : the one he calls the 

 Newcastle coal formation ; and the other the independent coal 

 formation : but for this division there does not appear to me any 

 sufficient reason, nor would it be easy, or indeed possible, to se- 

 parate these formations by any well-defined characters; for the 

 former is only the upper series of strata to the latter. The circum- 

 stance of galena veins occasionally occuning in the lower series 

 •will not entitle it to be considered as a distinct formation, by any 

 one practically acquainted with the coal district of our island 

 sbmtlh of the f v.'eed. 



When coal strata approach the metalliferous limestone, very 

 strong veins of galena will be found occasionally to penetrate the 

 coal, or to send up branches or strings of ore ; the more power- 

 ful veints generally rising the highest into the upper strata. Si- 

 milar instances might be cited in Derbyshire, Staffordshire, 

 'Lancashire, and other parts of England. As the whole of this 

 "district has been mined, and the succession and thickness of the 

 •strata ascertained, I shall proceed togive an account of Mr. Forster's 

 section, which includes, as before stated, a measurement of nearly 

 fourteen hundred yards But as the earth has nowhere been per- 

 forated to that depth in any ^one situation, persons not familiar 



* It is only nec^'-isary to use this lime moit spiuinti;ly. Inattention to 

 this circumstance gave rise to tiie opinion ot' its prejudicial effects on land. 

 I wfS inf' miec! I>y a farmei in Derbyshire, that though no vegetation will 

 'sprini; up for t" I) years, Avhere ii heap of the burnt magnebinn limestone 

 has been laid, after tluit time the place is always covered witl) an abun- 

 dant and vigorous crop of white clover. 



• with 



