240 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 5, 



With reference to the appearance of the axis on the opposite side 

 of the sandstone area, owing to the thick deposits of clay and gravel 

 which cover up both the red sandstone and the Silurians on the west 

 side of the valley of the Annan and the east flanks of the Tinwald 

 Hills, we lose sight of these deposits until we reach a spot called 

 Blaweary in the parish of Lochmaben ; and at this locality N.N.W. 

 dips show themselves, leading to the inference that the axis is to the 

 S.S.W. from this. In the course of the Bellridding Burn, in the 

 parish of Torthorwald, on the south side of the high-road, we meet 

 with both N.N.W. and S.S.E. dips, indicating a proximity to the 

 axis ; and in the same parish, in the course of the Peartree Burn, the 

 same circumstances are exhibited ; and here too the purple grits, 

 which constitute the axis, are also seen. From this locality west- 

 ward we lose all traces of both the axis and the Silurians themselves ; 

 but the former appears to strike in the direction of the syenitic 

 mountain Criffel in Kirkcudbrightshire. 



The course of the axis, as traced in Dumfriesshire, agrees with 

 that laid down by Professor Nicol in Roxburghshire, and supports 

 the inference that it has a E.N.E. and W.S.W. route through the 

 Silurians of the South of Scotland. 



The lithological nature of the strata composing the axis seems to 

 be the same throughout, consisting of purple grits which have great 

 resemblance to some of the bottom-rocks of the Longmynd. 



With regard to the strata which lie conformable to the axis on 

 both sides, they consist of thin-bedded greywacke sandstones, having 

 grey and purplish red shales interstratified with them. The pur- 

 plish-red shales are much more abundant in these lower portions of 

 the Silurians than in the strata more immediately connected with 

 the superior anthracitic and graptolitic shales ; and their presence 

 serves to mark a low zone in the Silurians of the South of Scotland. 



Although the strata most intimately connected with the axis oc- 

 cupy a considerable breadth of country on both sides of this axis, 

 there is reason to conclude that these beds do not attain any great 

 thickness, but that they owe their wide area to frequent repetitions 

 in consequence of flexures ; these flexures on the north side having 

 oblique curves towards the north, and the reverse occurring on the 

 south side of the axis ; in consequence of which we have almost uni- 

 form N.N.W. dips on one side and S.S.E. dips on the other. This, 

 however, is not universally the case ; for in the course of the Lamb- 

 ridden Burn in the parish of Torthorwald, on the north side of the 

 axis, both a N. and a S. dip obtain, in consequence of curving in 

 the strata, but the usual N.N.W. inclination soon succeeds. Like 

 circumstances are seen on the south side of the axis in the same 

 parish, at the farm of Barleiuth ; and a similar occurrence may be 

 seen in Eskdale on the farm of Billholm. 



The occurrence of flexures among these deposits is also exhibited 

 by the irregular angles of inclination, as well as by the comparatively 

 uniform characters of the repeated strata. 



There is another circumstance which tends to corroborate the in- 

 ference that the beds immediately contiguous to the axis have been 



