42 
THE CARBONIFEROUS VOLCANOES 
BOOK VI 
at tlu“Lrf 1 ,rr i ii e ° t that ; * s the . edges of the volcanic sheets emerge 
Ire c r ° l 'T n f e *— * — «« which these rocks 
extend must be considerably less than that which they originally covered 
T e fT°" iS S “» IW V outlieiTt 
position of f ’ aS W aS by b0SSeS Which d0llbtless indicate the 
remaiW r at P ■' tha erupfcive vents - The distance between the furthest 
material Jer!. heS ’V , Tbe ° ngmal tract over which the volcanic 
lleTbroad T? Ve he * a leSS than 24 miIes long b 7 10 
miles broad. If we assume its area to have been between 250 and 300 
square miles we shall probably be under the truth 
Sea ihi'jltr r T n ? Tt i tS , appearance 0n the *« of Carboniferous 
a in the same district which had witnessed the eruptions of Upper Old Eed 
Sands one time. The two visible vents that crown the Knockfeerina and 
i hapter XXii) ’ are onl y some ten miles distant, and 
f be ° the . rS 0f lh(: ; same a S e ev <‘» mider the Limerick basin. This 
district thus supplies another instance of that recurrence of volcanic enero-y 
‘he same area, after a longer or shorter geological interval, which standi 
out as a conspeuons feature in the history of volcanic actmn in BUtat 
pro onge interval elapsed between the extinction of the Old Eed 
.Sandstone volcanoes and the outbreak of their successors during the 
the thi t 1 f ? arb ° nifer0US Limestone s^ies, may be inferred from 
thickness of strata which separate their respective tuffs. From the 
500 tet Told Eed T S,, '' Ve >' there would appear to be about 
TPp , , T P 1 Sandsfcone above tlie volcanic series of that formation 
sle thfekness 6 V™ ^ which is computed to be about the 
same thickness from the scarcity of observable dip among the Lower 
unestones and their variable inclination, it is not easy to form any 
a isfactory estimate of the depth of this group up to the base of Z 
olcamc series. It may be as much as 800 feet/ and if so there would 
is lntci \ene a mass oi sedimentary material nearly 2000 feet in 
thickness between the two volcanic platforms. Throughout this thick 
accumulation of stratified deposits no trace of contemporaneous volcanic 
ac ivity has been detected. From the descriptions published more than 
SLL Ti ag °i y i u and MS C ° 1IeagUeS in the Geological Survey of 
lie and, geologists learnt how full and interesting are the proofs of g Lt 
volcanic activity contemporaneous with the deposition of the Carboniferous 
Limestone series in the Limerick district/ Nowhere, indeed, is the evidence 
Ireland n S 1 'a t j/ oblless 2* veu * u the Explanation to Sheet 144 of the Geological Survev of 
’ st' slianfv S TZ t,liCk “ eSS iS Claime '' 1,1 Ex P la -tion to Sheet 154, p = . 8 7 
U3 ’ I44> J 53 a, * d 1M ' Ge0L ^-Ireland (I860, 
writings reference made on y U ° tl0ed by earlier obsCTV er s , to whose 
T , 7 / on P- 2b of the Explanation of Sheet 144 See ,1 r . . , 
tZd'JTu V0h ( 1832 >> !'■ 24 i Prof. Hull, Geol. Mag, for im v Z Tl"’ 
if th . S.' 1 ' “? 
MM by Mr. Allpcrt, ™ Swt .’ST’/?*.'? 
Hull, Geol. Mew. for 1873 n K,q ,, ... p. , 552, and by Prof. 
the Collections of Rocks and Fossils (Dublin, 1895), p. 93 ‘ lu ' ollnt ol tl,ese rooks in the Guide to 
