14 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 28, 



carboniferous strata lying above the red measures of the limestones 

 of Ardwick down to the floor of the four-feet mine of Bradford, 

 Patricroft and Worsley*. It is 1560 feet in thickness, and contains 

 five workable seams of coal, the highest that have been wrought in 

 England. 



The second commences from the floor of the four-feet mine, and 

 terminates with the floor of the coal distinguished as the Riley mine 

 of Oldham, the Daubhill mine of Bolton, and the Arley mine of 

 Wigan, well-known as the last thick seam. In this division lie the 

 main coals. It is 2910 feet in thickness, and contains, according to 

 the testimony of Mr. Andrew Knowlesf (probably the oldest and 

 most extensive coal proprietor in Lancashire), twenty seams, which 

 I think may be termed workable ones. 



The third division includes all the strata lying between the floor 

 of the Riley mine and the limestone shales, and comprises all the 

 mountain mines. It is 2130 feet in thickness, and contains six 

 seams that have been worked. 



The upper field is best seen at Ardwick, where it can be traced 

 to within about 100 yards of the upper new red sandstone. In most 

 parts of the district it is not seen, being covered up by the upper new 

 red sandstone. Hitherto no passage of one formation into the 

 other has been observed. Its seams of coal and rocks, with the ex- 

 ception of the beds of limestone, are variable and difl^cult to trace 

 for any considerable distance. 



The coals and rocks in the middle field alter much in their cha- 

 racters]:, and are with difficulty identified at different points in the 

 county ; but the last thick seam, known by the respective names of 

 the Lower Woodley, Riley, Dogshaw, Daubhill, Arley and Orrell 

 mines, is well-known and easily identified. 



All the rocks and coals of the lower field are far more constant 

 than those of the other two, and there is little diflBculty in tracing 

 them through the whole country, and identifying them at the most 

 distant places. 



Most persons on inspecting the Lancashire coal-field are sur- 

 prised at the long narrow tongues of upper new red sandstone which 

 run into it. These are generally deep down -throws of the coal- 

 measures, which have been filled up with sandstone. Their direc- 

 tion is most frequently towards the north and north-west, but there 

 is one at Collyhurst near Manchester which runs a little east of 

 north. These faults, in the language of miners, " cut off"' the coals ; 

 but they are in fact down-throws ; and whenever they are found on 

 the rise of the mine, it may be taken as a general rule that the mea- 

 sures have been thrown down, although the sides of the fault, from 



* In a former communication I included all the Manchester coal-field in the 

 upper division, but I now consider that the four-feet coal is a much more con- 

 venient line for dividing the upper from the middle field. See Proceedings of the 

 British Association for Manchester Meeting (1842), Trans, of Sections, p. 49. 



t Memoirs of the Literary and Philosophical Society of Manchester, New Se- 

 ries, vol. vi. p. 452. 



J Proceedings of the British Association, anie cit. p. 50. 



