290 
Mr. Weaver on the 
discernible scales of white mica. It sometimes approaches nearly to 
the state of a quartzy sandstone, and contains frequent small con- 
temporaneous veins of quartz : and sometimes it includes thin streaks 
of slate clay. This district seems to be in a great measure deficient 
in the slaty micaceous sandstone, which abounds so much in parts of 
the Castlecomer coal district, particularly in the south-eastern quarter, 
and which affords excellent flags. 
§ 193* The fire clay under the coal varies from four to nine feet in 
thickness. It is of a blackish or bluish grey colour, more or less indu- 
rated and tenacious ; but on exposure to the atmosphere it soon 
disintegrates into a powder. Burnt in a strong fire, it becomes 
white and very hard. The whole substance of the fire clay is, in a 
manner, interwoven with vegetable impressions, apparently belonging 
to the grasses ; which, when fresh, have a rich, glossy, and almost 
silky aspect. 
§ 194. The coal of all this district, as well as of the other portions 
of the Leinster coal tract, is wholly of the nature of blind coal [an- 
thracite),* with a conchoidal fracture, strong lustre, and thin stratified 
structure. That of Coalbrook is in general very pure, and seldom con- 
taminated by iron pyrites ; and the specific gravity of a pure specimen 
is 1*61. The fire damp is entirely unknown throughout the Lein- 
ster coal tract. 
§ 195. At the distance of every forty or fifty yards, the Lisnam- 
rack coal seams are generally interrupted, by what are locally called 
hags, ranging across the troughs in a north-west and south-east 
direction. These hags are a partial substitution of firm shale in the 
room of coal, commonly from three to five yards broad, sometimes 
occupying nearly the whole thickness of the seam, but gradually 
diminishing and edging out in a north-east and south-west direction, 
the seam of coal then resuming its usual thickness. Above th® hag 
♦ Glanzkohl of Werner \ glance-coal, Jameson* 
