NATURE 



57 



THURSDAY, NOVEMBER 27, 1873 



THE SOUTHERN UPLANDS OF SCOTLAND * 

 II. 



THE next member of the series of rocks making up the 

 upper Llandeilo series in the Southern Uplands has 

 received from the officers of the Scotch Geological 

 Survey the name of the Lowther group. In its typical 

 area, which is in the N.W. of Dumfriesshire, this group 

 is composed of " fine grey shales and finely laminated fels- 

 pathic greywackes with occasional grit beds." The esti- 

 mated thickness of this group amounts to 5,000 feet. It 

 is seen overlying the Haggis rock group in the streams 

 which drain the upper portion of the Lowther hills ; with 

 the underlying Haggis Rock group it forms a synclinal 

 trough in which the Lowther hills are contained. 



In Wigtonshire the Lowther group rests upon the 

 Dalveen group. The strata here generally correspond with 

 those of Dumfriesshire, but shales are less abundant, and 

 flagstones and grit with shale bands become more deve- 

 loped. In this county, however, the proportion of the fine 

 and coarse rocks of this group varies in different localities. 

 The rocks of the Lowther group in Wigtonshire are best 

 exposed on the shores of the Irish Channel. Here be- 

 tween Morroch Bay and Knockienausk Head, cliffs are 

 seen from 100 to 300 feet high composed of strata often 

 very twisted and broken, belonging to the Lowther group ; 

 and in the higher portion of this group, where the flags 

 are well developed, they have been worked for roofing 

 and flooring purposes. 



Above the Lowther group, and forming the highest 

 member of the Lfpper Llandeilo series, as these occur in 

 the Southern Uplands, are strata composed of grey shales 

 with bands of fine-grained blue greywacke and flinty 

 mudstones. Numerous bands of dark anthracitic shales 

 with graptolites interstratify these rocks. These strata, 

 with their associated anthracitic beds, have received the 

 name of the " Upper Black Shale Group." Their esti- 

 mated thickness is about 3,400 feet. This Upper Black 

 Shale group occurs near the northern limits of the Upper 

 Llandeilo rocks, and is more abundantly developed in La- 

 narkshire than in Dumfriesshire. 



The Upper Black Shale group, in its typical area, has 

 yielded the officers of the Geological Survey a rich grap- 

 tolitic fauna, no less than 27 species having been obtained 

 from this series of rocks. These species bear a very 

 close resemblance to such as occur in the Moffat Shales, 

 a horizon much below the Upper Black Shale group in 

 position. Two Brachiopods have also been found in con- 

 nection with these Upper Black Shales, viz., Siphonotrcia 

 inicula, a form also occurring in the Moffat Shales, and 

 likewise in the Upper Llandeilo rocks of Wales, especially 

 in the neighbourhood of Builth ; and a Discina which 

 has not yet been specially recognised. 



The Upper Black Shales group, following the persistent 

 strike of the Upper Llandeilo rocks of the Southern Up- 

 lands of Scotland, makes its appearance in Wigtonshire. 

 Two bands of this group lying in a synclinal trough tra- 

 verse the portion of Wigtonshire contained in Sheet 3. 

 One of these bands is well seen in Morroch Bay, about a 



Continued from p. 24. 



Vol, IX.— No. 213 



mile and a half south-east of Port Patrick. The other 

 appears south-west of Stranraer, and crossing the moors 

 to the north-east, is seen in the bed of the Luce below 

 Cairnarzcan. In Morroch Bay the Upper Black Shale 

 group exhibits a threefold petrological nature. The higher 

 beds consist of thin black shales, having in them lenticu- 

 lar masses and seams of coarse clay, ironstone, and nodu- 

 lar layers of greywacke and pyritous kernals. The strata 

 here are much crumpled, and intrusive masses and veins 

 of felstone have invaded them. It is in this upper portion 

 of the group that graptolites occur, but the number of 

 species obtained from these strata is considerably under 

 what have been found in the Upper Black Shale group of 

 Lanarkshire. 



The representatives of the Upper Llandeilo rocks in 

 the Southern Uplands of Scotland attain to a very great 

 thickness. Of the lower portion of the series, the Ard- 

 well group, the Lower or Moffat Black shale group, the 

 Oueenberry grit group, the Hartfell group, and the Daer 

 group, the officers of the Geological Survey have not 

 given their thickness in Dumfriesshire. Of the other 

 four groups, the Dalveen, the Haggis Rock, the Lowther 

 and the Upper Black Shales, these have an estimated 

 thickness of 13,000 ft. If to this amount be added the 

 five groups below, we have a development of Upper 

 Llandeilo strata in the south of Scotland which must 

 amount to nearly 20,000 ft. This great thickness of strata 

 much exceeds the same series of rocks developed else- 

 where in the British Isles. 



The Upper Llandeilo rocks of the Southern Uplands of 

 Scotland have a greater uniformity in their mineral nature 

 than is usually common to the series. Greywacke in the 

 form of shales, sandstones, grit, and conglomerates, having 

 in some of their sub-divisions black shales containing 

 graptolites, constitute this great thickness of sedimentary 

 rocks. There is an absence of limestone strata, only 

 nodules occurring occasionally, and the calcareous flags 

 which are so characteristic of this portion of the Lower 

 Silurian in its typical area Llandeilo, have no representa- 

 tives in the South of Scotland. The rocks in this district 

 have been originally greyish and reddish muds, grey and 

 purple sands, and pebble-beds, with occasionally dark 

 carbonaceous muds, which may have derived their black 

 colour either from decaying sea-weeds or decomposing 

 Hydrozoa. The presence of carbonate of lime seems to 

 have been very rare in the Upper Llandeilo seas of the 

 areas which are now recognised as the Southern Uplands, 

 during the deposition of their strata, and to this great 

 absence of carbonate of lime we may probably attribute the 

 absence of some of the fossils which are so abundant ia 

 Wales in this series of rocks. Graptohtes are essentially 

 the characteristic fossils of the Upper Llandeilo of the 

 Southern Uplands. The same species seem to run through 

 whole strata from the Moffat Shales to the highest mem- 

 ber of the seriesjhaving a range of probably 1 8,000 ft. ; and 

 many of these forms of graptolites are common alike to 

 the Upper Llandeilo rocks of Wales and Scotland. 



The case is, however, very different when we come to 

 compare the Crustacea of the two regions. In Scotland 

 the Upper Llandeilo crustaceans are very few, and almost 

 confined to Phyllopods, being Peltocaris Harkncssi, P. 

 aptychoides, and Disinocaris Brownii, while in Wales we 

 have a considerable development of trilobitic life. Of the 



