519 
of Edinburgh, Session 1879 - 80 . 
the loss during a short interval considerably greater than the true 
average of a longer period. 
It occurred to me recently that data of at least a provisional 
value might be obtained from an. examination of tombstones freely 
exposed to the air in graveyards, in cases where their dates remained 
still legible or might be otherwise ascertained. X have accordingly 
paid attention to the older burial-grounds in Edinburgh, and have 
gathered together some facts which have, perhaps, sufficient interest 
and novelty to be communicated to the Society. 
At the outset it is of course obvious that in seeking for data 
bearing on the general question of rock-weathering, we must admit 
the kind and amount of such weathering visible in a town to be in 
some measure different from what is normal in nature. So far as 
the disintegration of rock-surfaces is effected by mineral acids, for 
example, there must be a good deal more of such chemical change 
where sulphuric acid is copiously evolved into the atmosphere from 
thousands of chimneys than in the pure ah’ of country districts. 
In these respects we may regard the disintegration in towns as an 
exaggeration of the normal rate. Still, the difference between town 
and country may be less than might be supposed. Surfaces of 
stone are apt to get begrimed with dust and smoke, and the crust of 
organic and inorganic matter deposited upon them may in no small 
measure protect them from the greater chemical activity of the more 
acid town rain. In regard to the effect of daily or seasonal changes 
of temperature, on the other hand, any difference between town and 
country may not impossibly be on the side of the town. Owing, 
. probably, to the influence of smoke in retarding radiation, thermo- 
meters placed in open spaces in town commonly mark an extreme 
nocturnal temperature not quite so low as those similarly placed in 
the suburbs, while they show a maximum day temperature not 
quite so high. 
The illustrations of rock-weathering presented by city grave- 
yards are necessarily limited to the few kinds of rock employed for 
monumental purposes. In this district the materials used are of 
three kinds: — 1st, Calcareous, including marbles and limestones; 
2d, sandstones and flagstones ; 3d, granites. 
I. Calcareous. — With extremely rare exceptions, the calcareous 
tombstones in our graveyards are constructed of ordinary white 
