94 Ohservaiions on the Geology 



ifrequent opportunities of seeing the whin-stone in contact with 

 coal. Similar effects, I am informed, may be noticed in many 

 if not in all the coal mines of this district, where the whin-stone 

 immediately cuts through the coal. The whin-stone is inter- 

 sected by fissures, and divided into blocks nnd balls: in some 

 parts it graduates from basalt into an iron clay, Avhich in one 

 situation I saw formed into groups of minute regular pentagonal 

 prisms : some of these 1 brought away with me. The whin- 

 stone of this dyke contains numerous small cavities filled with 

 olivine ; hut in no specimens that I have seen from the dyke at 

 Coaly Hill are there anv cavities filled with chalcedony. I am 

 therefore inchned to believe that the basalt laid on the road 

 which Dr. Thomson saw, was not from this place, as a great 

 variety of basalts and other stones are constantly brought from a 

 distance as ballast to Newcastle, and employed for the roads. 

 In some of these I have seen both chalcedony and zeolites. 



Theie is a dyke filled with loose sandstone or rubble, which 

 crosses a considerable part of the coal field without any disturb- 

 ance of the strata. This, I believe, has been a mere fissure filled 

 from above by materials washed into it. A similar dyke or 

 fissure occurs in the Bradford coal field near Manchester, of 

 which I have given an account in the second volume of the 

 Transactions of the Geological Society. 



Though I have spoken of the east and west basalt dykes as ex- 

 tending from the sea westward, I believe it would be more cor- 

 rect to describe them as streams of basalt diverging from a cen- 

 tral focus in the mountains of Cumberland and Westmoreland 

 beyond the mountain called CroES Fell. The summits of some of 

 the mountains nearUlswater, particularly Swarthfell, are covered 

 vith basalt of a similar kind. On the western side of Northum- 

 berland the basalt rises in vast masses to the surface, and assumes 

 the columnar form. In a direction towards the same focus may 

 be traced the most considerable basalt dyke at present known in 

 England, extending through the county of Durham and the 

 north riding of Yorkshire to the sea between Whitby and Scar- 

 borough, of which a further account will be given in the second 

 edition of my Introduction to Geology, now in the press. It is 

 the same dvke which passes through the coal mines at Cockfield, 

 and has produced the remarkable effect of charring the coal, and 

 coating the under surface of the stratum above the coal with 

 crvstals of sulphur described in Mr. Bailey's Survey of Durham. 

 The apparent agency of fire upon the coal extends to fifty yards 

 on each side of the dyke. The Burtreeford dyke runs nearly 

 north and south. These dykes, and the remarkable peculiarities 

 of the metallic veins on the western side of Northumberland and 

 Durham, offer a rich field to the labours of future geologists, 



but 



