Professor Epwarp Hutu—On the Nature and Origin of Beds of Chert. 73 
Geological Structure.—The Carboniferous Series from the coal-measures down- 
wards are generally divided as follows :— 
Trish Divisions. British Representatives, 
Stage F. Middle Coal-measures (Tyrone), . . Middle Coal-measures. 
» EE. Lower do., or “ Gannister Beds,” . . Lower do. or Gannister Beds. 
» D. Millstone Grit, and Carlow Flags, . Millstone Grit. 
», C. Upper Shale series, ; . 6 » Yoredale Beds of Upper Lime- 
stone Shale. 
Upper Limestone, 
; i Mountai 
» B.< Middle do. or “ Calp Beds,” CERIO an oem 
F Limestone. 
Lower Limestone, ramen 
» A. Lower Carboniferous Slate, . : Lower Limestone Shale or 
Grit and Conglomerate, 6 ome) Tweedian Series. 
From the above table it will be observed that the Carboniferous Series of England 
- and Wales has its exact equivalents in Ireland, although the series in Ireland is 
less developed in its upper stages than in some parts of Britain, and there are 
slight differences in the mineral characters of the correlated strata. This subject I 
have dealt with more fully in another place.* TI shall, therefore, content myself 
with some account of that member of the series with which we are immediately 
concerned on this occasion, viz.—the Carboniferous Limestone. 
The great series of limestone strata included under this name rests (when the 
series is complete) on the Lower Carboniferous Slate of the south of Ireland into 
which, as the late Professor Jukes has suggested, the formation passes laterally as 
well as vertically towards the western shores of Kerry and Cork. In the north of 
Ireland, however, the basement beds of the Carboniferous system consist of grits, 
conglomerates, and shales with bands of earthy limestone (Mayo), the whole 
similar to the “Calciferous Sandstone Series” of Scotland, which is its exact 
representative in time. The Carboniferous Limestone itself is generally divisible 
into three members, as shown above, of which the central is the least persistent 
and characteristic. In the county Galway and the barony of Burren in the county 
Clare the central member is either absent, or so resembles the other two members 
as to be inseparable from them, and the whole formation of 2,120 feet in thickness 
consists of beds of limestone with two cherty zones, the upper at 1,500 feet from 
the top of the formation, the lower about 400 feet from: its base,{ but in other 
parts of the country, especially towards the north and east, the three divisions are 
sufficiently distinct so as to present well-recognised physical features capable of 
* This subject is treated in detail in a paper read before the Geological Society of London (25th 
April, 1877). ‘On the upper limit of the essentially marine beds of the Carboniferous System of the 
British Isles, &c.” Quart. Journ. Geol. Soc., Nov. 1877. 
7G. H. Kinahan. “Explanation” to sheet 124 of the Geol. Survey Maps, p. 10, 1876. 
+ G. H. Kinahan. “Explanation” to sheets 115 and 116 of the Maps of the Geological Survey of 
Treland, p. 11. EE. of Loughrea the Calp or Middle Division can be recognised. 
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