﻿210 DE. H. c. soKBY oiiT THE applicatio:n^ OF [May 1908, 



in connexion with the present condition of the rock. Many of my 

 experiments were made with bnilding-stoue, in order, if possible, 

 to obtain some clue to the cause of their variable durability ; 

 but I will mass them together, and g:ive such results as are of 

 geological interest. 



&' 



Sandstones. — First of all, we may compare the sandstones of 

 New Red, Carboniferous, and Old Red age, of which I have 

 examined a fair number, but only from a few districts, so that 

 my results cannot be looked upon as necessarily applying to every 

 place. Those of ISTew Red age were from Maer in Staffordshire, 

 and Mansfield in Nottinghamshire. Leaving oat a shaly bed, the 

 mean for the different places near Maer is 25 per cent., which 

 agrees closely with the minimum for spheres and for fairly-uniform 

 grains of sand. The variation from 21*5 to 2S"8 may be explained 

 by variation in the grains and the presence of a small amount of 

 infiltrated carbonate of lime. The very friable sandstone at Mans- 

 field, in which the rock-houses were excavated, contains 33'5 per 

 cent, of vacuities ; which looks as though the grains had never 

 completely accommodated themselves to the smallest volume. The 

 very special and excellent building-stones contain on an average 

 only 16*9 per cent, of vacuities, and thus approach closely to the 

 building-stones from the Old Red of Herefordshire; like them, 

 the greater solidity is due partly to infiltrated calcite, and partly 

 to deposition in deeper water, with less sorting of the material by 

 bottom-currents. 



The sandstones of Carboniferous age were from South Yorkshire, 

 Derbyshire, and the Forest of Dean. The vacuities vary from 

 8'7 to 14'8 per cent., the mean being ll'l. This small amount is 

 sometimes due to the original cavities having been, to a con- 

 siderable extent, filled up by decomposed felspar ; but sometimes it 

 may be ascribed to the feebleness of the bottom-current. 



The Old Red specimens studied were building-stones from various 

 quarries in Herefordshire; and, leaving out those containing an 

 unusual amount of carbonate of lime, the vacuities vary from 

 16*1 to 21 per cent., the mean being 18'4. In those containing 

 much carbonate of lime, some of which are building-stones of 

 remarkable durability in pure country-air, the cavities have been 

 to a large extent filled up, and the mean is only 6 per cent. This 

 infiltration and the greater depth of water and less bottom-current, 

 and also exposure to pressure for a longer time, will explain why, 

 on an average, there is a marked difference between the sandstones 

 of Old and those of New Red age. 



The Gannister near Sheffield is, in some cases, an excellent 

 example of the almost complete filling-up by infiltrated quartz 

 of the interspaces in a deposit of very fine sand. When fractured 

 surfaces are examined with a microscope, many small crystals 

 may be seen. The boiling-water method shows that, in some 

 specimens, free from the rootlets of Stigmaria, the empty cavities 

 amount to less than 1 per cent., which is far below what occurs in 



