G. 11. Kinahan — On Faults in Strata, 119 



of Lonf>;h Corrib, Co. Galway, tliore arc Silurian rocks deposited 

 against clift's of Motamorpliic rocks.' 



In the places enumerated there are good data for the maj^ping of 

 faults, if the relative dips and strikes wore alone considered ; how- 

 ever, in none of the places mentioned are the normal positions of the 

 groups or varieties of rocks changed by faults or dislocations. In 

 the King's Co., Tipperary, Clare, Galway, and Kerry, wherever a 

 section near the base of the cliffs is exposed, the old shore-conglo- 

 merate occurs, over which the other rocks were deposited. Tliese 

 younger rocks — irrespectively of those with which they are in juxta- 

 position — sometimes dip away from the cliffs ; in other places they 

 are horizontal, while often they dip towards them. The last-named 

 position would be quoted, by some geologists, as evidence of a fault ; 

 however, no dislocation is necessary, for if the younger strata, after 

 deposition, were twisted or contorted, parts of them would almost 

 certainly have been so disturbed that they would now dip towards 

 the cliffs, while originally they were deposited horizontally, or dip- 

 ping away from the cliffs. In the Co. Limerick faults might be also 

 inserted, as in places the " Derivate - rocks "^ occur, striking up 

 against the "Ingenite rocks ;"^ but if the country is properly examined, 

 it will be found that higher beds are continuous over both classes, 

 proving that the " Derivate-rocks," which strike against the Igneous- 

 rocks, were deposited in hollows, or against cliffs. 



Although friction- surfaces generally occur in the fault-lines, if it 

 is a simple faxxlt, or on the two walls, if the line of break is marked 

 by a dyke of "Fault-rock"* yet in some instances none can be 

 observed, all traces having been obliterated by a subsequent action. 

 Tf rocks, after being faulted, are metamorphosed, the Fault-rock may 

 be cemented to the adjoining rocks, and thereby make a compact 

 mass, which will be easier broken anywhere than along the original 

 walls of the dyke or vein of Fault-rock. As such cases seem to be 

 the only exceptions to the rule as laid down by Mr. Medlicott, they 

 appear to add weight to it ; moreover, even in them the obliteration 

 of the friction-surfaces is not universal ; for if the original Fault-rock 

 were flookan, or any flaky stuff, the subsequent metamorphic action 

 would be almost sure to have altered it into a schistose rock, with 

 a foliation parallel, or nearly so, to the walls of the dyke, and thereby 

 not disturbing the features of the original walls, except, perhaps, 

 by modifying the termination of the planes of foliation in the 

 adjoining rocks. 



VII. — The Water-Bearing Strata in the Neighbourhood of 



Norwich. 

 By John E. Taylor, F.G.S., etc., and A. W. Mobant, F.G.S., etc. 



THE extensive excavations for sewerage purposes, which have been 

 going on for nearly two years, have brought to light several 

 peculiarities in the relative water-bearing properties of the various 

 strata in the neighbourhood of Norwich. 



^ Geological Map of Ireland, Sheet 95. ^ Sedimentary rock-? — Edit. 



3 Igneous rocks ? — Edit. 



* The rock made up of the debris of the rocks through which the fault passes. 



