J. G. Gooclchild — Weathering of Limestones. 463 



the anterior margin of the shell, was either not exposed, or broken 

 away at the time of deposition, the conclusion at which he arrived 

 was a very natural one-, though not in accordance with the results of 

 further investigation. 



VIII. — Notes on some Observed Eates of Weathering of 



Limestones. 



By J. G. Goodchild, F.G.S., of H.M. Geol. Survey, 

 Lecturer on Geology at the Heriot "Watt College. 



IN the Geol. Mag. for July, 1875, p. 326, the writer of the present 

 note gave some data bearing upon the rate of weathering of 

 certain limestones of the Lower Carboniferous Series, deduced from 

 the observed extent of waste that had affected some dated tombstones 

 in Kirkby Stephen Churchyard. The series of observations of which 

 that formed a part were suggested several years previously by the 

 fact that many of the rough blocks of limestone used for walling in 

 that neighbourhood had evidently suffered considerable waste since 

 the erection of the walls, and this especially on the upper and outer 

 surfaces of the stones referred to. In a few of these cases (as well 

 as in many other cases observed since) it was perfectly evident that, 

 since the coping stones had been placed in their present positions, 

 the waste of the limestone by atmospheric causes had proceeded to 

 at least as much as a quarter of an inch. This was evident from 

 the fact that thin, delicate, fragments of Corals, Brachiopods, 

 Encrinites, etc., were left standing out in sharp relief to that extent 

 above the general surface of the adjoining limestone matrix. There 

 could be no doubt about the fact itself, or about its significance : but 

 many inquiries failed to bring to light any reliable information 

 regarding the precise date when the stones were first quarried. For 

 aught we could say to the contrary, any one, or all, of the stones 

 might have been employed for building purposes for hundreds of 

 years previously ; although that was hardly likely. 



Similar phenomena were observed along the walls of the North 

 Western Eailway between Teba and Shap ; but regarding the earlier 

 history of these no reliable information could be obtained. 



With the tombstones above referred to the case was different. 

 Here we had stones that had been carved out of solid, unweathered 

 limestone at a given date recorded upon the tombstone itself, and 

 side by side with the date was given, by the hand of Nature, a 

 fairly exact record of the amount of limestone that had been carried 

 away in solution from the general surface of each of the tombstones 

 in question. The mean of several observations gave as the rate of 

 solution about one inch in five hundred years (Geol. Mag. 1875, 

 p. 326). These observations were made upon tombstones standing 

 erect, and therefore in the least favourable position for the kind of 

 erosion under notice. Where similar stones were lying flat, waste 

 by atmospheric causes almost certainly proceeded at a higher rate : 

 but no dated tombstones in this position could then be found. In 

 the estimate just given no account was taken of the fact that other 



