Kinahan — On Irish Arenaceous Rocks. 513 



hard as a silicious grit. Some stones contract considerably during the drying, and 

 stones of this class, before being used, ought to be given time to dry and contract, as 

 otherwise they will dry unevenly, and show not only unsightly open joints in the work, 

 but are also liable to cause uneven settlements.] 



The cements of the sandstones are silicious, calcareo-silicious, 

 and argillo-silicious. Usually in a contrary order they cut the 

 more easily, while their durability is the reverse, except in some 

 cases, that is, where they are micaceous, as many such stones, 

 otherwise good, are not durable. 



Other examples of well-preserved sandstone carving, besides the 

 previously mentioned doorway at Maghera, Co. Deny, are exem- 

 plified in the doorway at Killeshin, Co. Carlow, cut in the local 

 coal-measure sandstone ; in the massive and beautifully carved 

 crosses at Monasterboice, Co. Louth, the stone being a clean- 

 grained silicious sandstone, St. John's Grate, Drogheda, in the 

 same county, was built of mixed limestone and sandstone, and it 

 exemplified the unequal weathering and durability, the latter 

 being perfect, while the others have decayed considerably : it must, 

 however, be allowed that the limestone was of a very bad class. 

 The dressed work at Mellifont shows the durability of the sand- 

 stone. In the latter the bad effects of mica is also exemplified, 

 the micaceous sandstones that were used having sadly weathered. 



[The old ruins at Mellifont, during the late repairs under the Board of Works, had 

 the rubbish removed, and, as pointed out by Mr. Lynani, County Surveyor, the sand- 

 stones thereby re-exposed have rapidly weathered. This I have observed elsewhere, 

 not solely in regard to sandstone — as the stones in different ruins, when exposed to the 

 drying effect of the atmosphere, have rapidly decayed. This may be seen, as well as 

 elsewhere, at Devenish, Lough Erne, where the re-exposed sandstones have suffered, 

 and in St. Kevin of Glendalough, Co. Wicklow, where many of the old disentombed 

 sadptured schist slabs have, in a few years, been greatly defaced. A cupped stone, 

 now in " Saint Kevin's Kitchen," when first raised, had all the tool markings; but 

 these were obliterated by its being allowed to weather for a year. It may appear re- 

 markable that stones, when in their natural saturation, that is, having their " quarry 

 water," harden when exposed, while stones subsequently saturated, when dried, de- 

 cay. To explain this, it may be suggested that the first water, that is, the " quarry 

 water," was in combination with either silica or carbon, the mineral matter consolidat- 

 ing as the water evaporated, while in the subsequent saturation, the moisture was 

 solely water that had saturated the pores and other vacancies in the stone, thereby ab- 

 sorbing the cement, and when this water with the absorbed cement was withdrawn, it 

 left the stone more or less a friable mass — at least as far in depth as the absorption had 

 effected it.] 



