448 Geological Society. 



formerly placed in St. Mary's Abbey at York, which were recently 

 discovered in digging the foundation of the Yorkshire Museum. 



The more rapid waste of those parts of a building which are shaded 

 by a projecting ledge, is compared with analogous effects upon de- 

 tached blocks of stone (like the Buckstone near Monmouth), which by 

 a further continuation of the process might be transformed into rock- 

 ing-stones, as at Brimham Crags in Yorkshire. The rapid waste oc- 

 casioned by fluctuations of heat and moisture is next examined ; and 

 it is shown that the south and west fronts of buildings suffer most by 

 these variations j that when the composition of the stone is unequal, 

 the waste of its surface corresponds in general to the nature and ar- 

 rangement of the particles j but that also there are cases when the 

 atmospheric influences cause an exfoliation of the surface, without 

 reference to the internal arrangement of the particles. Thus, de- 

 squamation is observed to happen parallel to the ornamented sur- 

 face of the sandstone balusters of a bridge at Durham, to the rounded 

 face of the " flagstone" employed for curbstones at York, to the em- 

 bossed tooling of the "molasse" used in the walls of Zurich, and to 

 the west front of the magnesian limestone of a church in Yorkshire. 



The power of frost in connection with other agents is then noticed 

 as very important in producing the fall of mountain precipices ; and 

 the author concludes his paper with a description of some remarkable 

 excavating effects of rain on the surfaces of ancient monumental 

 stones and bare limestone rocks. He endeavours " to show, that 

 within the historic aera hard and durable stories have been greatly 

 furrowed by the rain, and that in more ancient periods the precipita- 

 ions from above have carved themselves channels of various kinds, 

 and sometimes occasioned real though miniature valleys of great 

 length and continuity." 



The first example of these rain channels is taken from the druidi- 

 cal stones of Boroughbridge, composed of millstone grit, called the 

 Devil's Arrows ; and it is shown that the rain beating upon these vene- 

 rable pillars, has cleft their tops and furrowed their sides, in the lines 

 of quickest descent, without regard to the irregularities of their com- 

 position. One of the stones leans remarkably and threatens to fall ; 

 but an examination of the rain channels shows the inclination of the 

 stone to be of most ancient date, for these descend further on the 

 upper sloping face than on the under. 



Stones which have fallen from the limestone cliffs of Switzerland 

 have been furrowed by the rain since the time of their descent. 



On Doward Hill near Monmouth, and still more in the broad sur- 

 face of the crags around Ingleborough in Yorkshire, the effects of the 

 rain on the weathered beds of limestone are evident and remarkable. 

 But the most striking phenomena of the kind known to the author 

 occur on Hutton roof crags near Kirby Lonsdale. 



Hutton Roof Crags afford an opportunity of tracing the rain chan- 

 nels over an immense surface of bare limestone rocks, lying nearly 

 level on the hill- top, but sloping rapidly down the sides to the east 

 and south. On the level top of the hill the stones are variously 



worn 



