242 Mr. Williamson on the Limestones found 



terest in itself further than a few plain sections can afford, if 

 we except the salt mines of Cheshire. Concerning these, as 

 well as the variations of colour, much has yet to be learnt; but 

 the young student finds these questions too difficult to grapple 

 with, and the chief objects which would render the investiga- 

 tion more pleasing to him, organic remains, are entirely 

 wanting. 



The northern side of the town is bounded by the vast series 

 of the Lancashire coal strata, which are always interesting, and 

 have consequently received a proportionate degree of attention, 

 especially from my friend Mr. Francis Looney; but the line 

 of junction between the saliferous and carboniferous groups 

 has been so little investigated, that the result has been an 

 error respecting the nature and position of a series of lime- 

 stones which have now become the most interesting portion of 

 the geology of the district. This error is highly excusable, on 

 account of the difficulty of obtaining sections of the strata. 

 The surrounding country is so level that no natural ones can 

 be obtained except on the banks of the Medlock at Ancoats. 

 Human labour has exposed others on the line of the Liverpool 

 railway and at the pits near Ardwick, where some of the lime- 

 stones are worked, but these must be viewed in detail. 



Mr. Elias Hall, in his geological map of Lancashire, has 

 represented, by a green line, a series of limestones, under the 

 general head of magnesian, passing eastward of Stockport, 

 round the eastern and northern sides of Manchester, and ex- 

 tending in an undulating direction to the western coast of Lan- 

 cashire, near the village of Crosby. But here he seems to 

 have laid down the line with more distinctness than the ap- 

 pearances will justify, as there are few points on the range 

 where any limestones are visible, and at three of the points out 

 of five, from Manchester to the coast, a limestone connected 

 with the coal-measures has been mistaken for and confounded 

 with the true magnesian limestone. These two we must ex- 

 amine separately, the magnesian and the carboniferous series, 

 and as we proceed, we shall detail the circumstances which 

 induce us to differ from Mr. Hall's views. 



Sect. H. Magiiesian Limestone. 

 This stratum is but little exposed in this neighbourhood, 

 appearing only at two localities, Collyhurst near Manchester, 

 and Bedford near Leigh, between Manchester and the sea- 

 coast, at both of which localities the exposed portion is ex- 

 ceedingly circumscribed, and had we only been guided by ex- 

 ternal appearances, we should have hesitated long ere we 

 identified the tbin variegated deposit of Lancashire with the 



