12 LOWER COAL MEASURES BETWEEN BAGILLT AND HOLYWELL. 
mountain, where so many lead veins are mapped, as the true 
representative of that formation. It is in this strip that the 
Chert Beds are found; and I cannot help thinking that these 
beds are really a particular condition of the millstone-grit. 
In the neighbourhood of the Minera Mine, near Wrexham, 
almost every gradation, from a coarse sandstone to true chert, 
may be found ; and the terms millstone-grit and chert are almost 
convertible among the more educated lead miners. 
About one mile North of the cement-stone quarries, and 
behind Greenfield Hall, is a large flag-stone quarry. These 
beds consist of numerous strata of coarse micaceous sandstone 
from about 2in. to 1ft. thick, and containing Anthracosia, and 
casts of worm burrows, suggesting a more brackish water 
formation than the last. This is also higher up in the series, 
coming near the coal-bearing measures, though it is also 
coloured in the map as millstone-grit. Here again it seems 
probable that the valley by Holway Mine is the true boundary 
between the coal-measures and the millstone-grit. 
[Since the above Paper was read, my friend Mr. Srrawan 
has found an unmistakable millstone-grit Breccia in the 
“narrow strip” referred to above. | 
