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and sometimes sulphuret of iron, which are scarcely to be seen 
in the white sandstone when first obtained from the quarry, 
but on exposure to the atmosphere the iron becomes further 
oxidized, and the stone “bleeds” and becomes discolored, as 
well as decomposed. It may be safely concluded that there 
is no quantity of good building stone, suitable for outside 
building in a city like Manchester, to be procured from the 
middle coal field. 
The lower coal field and the millstone grit yield the only 
good building stones for Manchester. These strata comprise 
the beds lying under the Arley or Royley seam of coal and 
the limestone shale, and from their being generally found on 
the high land of the district, are known by the name of 
“ High Moor Stone.” 
As all the lower coal field and millstone grit beds have 
most probably been formed of the debris of granite or 
granitoid rocks, we find in them the proportions of silica, 
alumina, potash, iron, lime, and magnesia generally met with 
in those rocks. As a general rule the more pure silica the 
rock is composed of, the better building stone it is. A 
mixture of mica or clay causes the rock to be more schistose 
or flaggy, as well as softer. Two chief beds of flags, besides 
several smaller ones, occur in this division, namely, the upper 
flag of Upholland, Catlow, and Holy Fold, lying between 
the Arley and Royley coals, and the lower flag or Brad- 
shaw and Shawforth near Rochdale, lying under the rough 
rock and above the upper millstone grit. These flag beds 
yield the stone generally used for par point work. 
A fine sharp grained silicious grit is found sometimes above 
the gannister coal, as at Ending Common near Rochdale, 
which makes a good building stone. 
A stone much used in building is the Halliwell, Woodhead 
Hill, or Lomax Wood rock, lying immediately under the 
salts or best coal of New Mills. 
The rough rock, generally known as Summit and High 
