J. G. Goodchikl — Weathering of Limestones. 465 



as if the rock bad been steeped in weak acid. The characteristic 

 glaze, due to the redeposition of thin films of carbonate of lime, 

 imparted a curious artificial appearance to the stones. But the most 

 remarkable feature was the projection of delicate portions of corals 

 and other organisms in sharp and high relief above the general 

 surface of the weathered stones. It was perfectly evident that, 

 since the road had ceased to be used as a cart road, the surface- 

 waters had etched away the limestone to a depth of at least one- 

 sixth of an inch, leaving the sharp edges of the fossils standing out 

 to that extent in relief, to testify to the quantity of the surrounding 

 matrix that had been dissolved and carried away in the mean time. 

 One could not feel sure that the slender, delicate, edges of the 

 projecting fossils afforded correct data for determining the original 

 surface exposed ; but assuming that they did so, and that no more 

 had been removed than we can now estimate from these data, the 

 present state of the stones in question proves that even bituminous 

 limestone may be dissolved away by atmospheric agencies at the 

 rate of one inch in two hundred and fifty years. Here again we 

 have to take further into account the accelerated waste consequent 

 upon the development of additional planes of solution along the 

 bedding and the bate. 



Another case in which an approximate estimate of the quantity 

 of limestone removed by atmospheric causes in a known time 

 occurred near Penrith several years ago. In one of the cuttings on 

 the Keswick Kail way just south-west of Penrith, a bed of limestone 

 belonging to the Yoredale Series was bared of glacial drift for a 

 short distance. When newly exposed, the limestone presented the 

 usual appearance of a striated and smoothly-polished surface, with- 

 out a trace of any asperities due to projecting fossils. An exposure 

 to the weather for a period of only ten years sufficed not only to 

 roughen the surface of the limestone, but to lower the general 

 surface of the rock to such an extent that some of the more durable 

 fossils were left standing about one-thirtieth of an inch in relief. 

 In other words the limestone was wasting away along that surface 

 alone at the rate of one inch in three hundred years. In the present 

 case the water affecting the stone must have been almost entirely 

 free from any admixture derived from decomposing vegetable matter, 

 and the rock surface must have remained dry except during showers. 

 [At Blenoo Station, just beyond, a slab of sandstone beautifully 

 glaciated has been exposed to precisely the same conditions for about 

 25 years ; but it shows no signs whatever of having undergone any 

 waste in the mean time. The contrast between the behaviour of the 

 two kinds of rock in this, as in the majority of the other cases that 

 have come under my notice, is most striking and instructive.] 



Within the last month (August, 1890), another illustration of 

 an equally instructive nature has been observed. Twelve years ago 

 the new railway between Leyburn and Hawes, in Wensleydale, was 

 in process of construction, and the contractors naturally took 

 advantage, wherever they could, of any quarries of building stone 

 suitable for their requirements. When the station at Askrigg was 



DECADE III. — VOL. VII. — NO. X. 30 



