COAL. 307 



there are twenty sandstone beds, besides alternations of 

 shales and clays. In the Durham and Northumber- 

 land coal-field, forming a mass 4,035 feet in depth, 

 there are said to be thirty-two beds of coal, sixty-two 

 of sandstone, and, towards the bottom, seventeen of 

 limestone ; the remainder consisting of shales and clays : 

 a bed, or pseudo-stratum, of basalt being in one place 

 interposed, as an adventitious and accidental rock. One 

 foot and a half is an average of the thickness of the 

 coal beds, and six feet the largest dimension. It is 

 unnecessary to gi\ r e more examples of the disposition of 

 coal in England. 



In Scotland, there are but two coal-fields of this na- 

 ture; and, as far as I can here venture to mark a diffe- 

 rence, it is that the proportion and range of the coal 

 beds in the total series is less than in equivalent spaces 

 in England. In general, the usual alternation of strata 

 succeeds to the red sandstone, and to a limestone ana- 

 logous to the mountain limestone of English geologists. 

 But this is sometimes absent ; so that the coal series lies 

 immediately on the red sandstone. But the strata which 

 follow it in England are here wanting; so that it is the 

 uppermost where it exists; though small portions of 

 the rnagnesian limestone and of the red marl have been 

 said to occur in some places. I need not give special ex- 

 amples of recorded variations, especially as I am by no 

 means satisfied of the correctness of the observations. 



In Ireland, the Connaught coal strata lie, similarly, 

 on a body of limestone of various character, sometimes 

 interstratified with sandstones, and following the lowest 

 red one : the series terminating upwards in the shales 

 and sandstones. In the Leinster district, a similar 

 limestone is said to repose on the granite, and to be 

 followed by a corresponding succession of beds. But 

 I. need not enter into further, and sometimes doubtful 



X 2 



