248 C. LAPWORTB. ON THE MOFFAT SERIES. 



height. Near its centre it is joined by a second gorge, narrower and 

 deeper, and terminated abruptly by a precipice of grit. Above the 

 precipice two small streams draining the moory mountain-tops to 

 the west unite, and hurl their waters down the cliff in two succes- 

 sive leaps to the bottom of the chasm, which, like the longitudinal 

 hollow itself, has been excavated wholly in the black and grey 

 shales of the Moffat Series. 



This picturesque cascade, which is known as Dobb's 'Linn, gives 

 its name to the whole glen. Like many of the deep rugged gorges 

 that relieve the smooth undulating monotony of the Uplands, the 

 place has its legends of the Covenanters, bloody and quaint, so that, 

 apart altogether from its weird scenery, the spot has long enjoyed a 

 local reputation. 



To the geologist visiting the glen for the first time the section of 

 the shales and mudstones afforded by the northern cliff of the 

 lateral gorge is that which, above all others, commends itself to his 

 notice, as it is visible from end to end, and, exception being made of 

 a few local contortions, the strata exhibited appear to follow each 

 other in natural and unbroken sequence. The coarse grits and 

 flagstones of the falls dip at 70° or 80° to the east, and plunge 

 visibly beneath a thick series of grey shales with black bands. This 

 group is followed first by a group of black shales, and next by a 

 similar thickness of greenish-grey mudstone. Upon the latter reposes 

 a second series of black shales, much thicker, and quite distinct in 

 its general features from that already noticed, forming clearly the 

 final member of the Moffat Series as here exhibited, and passing 

 beneath the greywackes of the eastern cliffs at a low angle. So 

 clear are these facts, and so obvious the conclusions to which they 

 point, that no one would hesitate to infer that the Moffat beds of 

 this locality constitute a single band of fossiliferous shales and 

 mudstones, composed of three members, and actually interbedded in 

 the great barren greywacke series. (Plate XII. Section I.) 



If, however, we select any one of the well-marked zones of black, 

 white, or green mudstone so conspicuously exhibited at this spot, 

 and follow it carefully in its outcrop, first up the south cliff, and 

 thence across the face of the steep slope on the right-hand side of 

 the longitudinal gorge, it will be ascertained that it gradually 

 undergoes a complete reversal of its original inclination, until, 

 finally, in a magnificent cliff-section about 100 yards from our 

 starting-place, all the zones we have recognized in the lateral gorge, 

 together with others not there apparent, and inclusive also of the 

 coarse grits and flagstones of the waterfall itself, are now arranged 

 in the opposite order, and dip steadily at a gentle angle to the 

 W.N.W. 



Thus, in the two chief sections of the glen, the order of succession 

 deduced from the evidence afforded by the one is completely contra- 

 dicted by that of the other. It is clear that in one of these sections 

 the strata must be inverted ; and we are thus taught at the very 

 outset of our inquiry how utterly futile is the endeavour to deter- 

 mine the original sequence of these deposits merely by attention to 



