Nov. 13, 1 873 J 



NA TURE 



23 



form of an anticlinal axis near the southern border of the 

 Silurian area. This axis can be well seen in Roxburgh- 

 shire and Dumfriesshire, having a north-east and south- 

 west direction. It has also been recognised by the 

 officers of the Geological Survey in Wigtonshire ; and the 

 rocks which it exhibits, which are the lowest in the 

 Southern Uplands, have been designated by Prof. Geikie 

 the " Ardwell group." This group is made up of " hard, 

 well-bedded greywackes and grits, with bands of hard 

 shale or slate. These rocks have a prevailing reddish or 

 brownish hue, especially on weathered surfaces." 



As seen in Dumfriesshire and Roxburghshire these 

 low rocks have the same aspect and nature. They have 

 afforded, both in Wigtonshire and Dumfriesshire, mark- 

 ings which have considerable resemblance to the fossil 

 described by P.IcCoy as Protovirgularia, and in Roxburgh- 

 shire they have yielded crustacean tracks, but no other 

 traces of organic remains have been obtained from them. 

 Above the Ardwell group the officers of the Geological 

 Survey recognise a mass of strata to which they have 

 given the name of the " Lower or Moffat Shale group." 

 This group is composed of '"' flaggy grey wacke and grey 

 shales," which are distinguished by the occurrence in 

 them of several bands of black carbonaceous shales. 

 These strata are well developed in the neighbourhood of 

 Moffat, Dumfriesshire, from whence they derive their 

 name. The black carbonaceous shales are very per- 

 sistent, having been traced by the officers of the Survey 

 from near Melrose to the ivestern shores of Wigtonshire, 

 " a distance of more than 100 miles." Three bands of 

 carbonaceous shales can frequently be made out, but 

 occasionally they come together so as to form one thick 

 band. These bands are very prolific in graptolites. They 

 have, from their carbonaceous aspect, induced many 

 persons, under the guidance of " practical miners," to 

 expend large sums of money in search after coal, and 

 some of the spots where they have been worked are 

 known under the name of " coal heughs." 



Although the Moffat group is well developed 

 through the greater portion of the Southern Up- 

 lands, it is on the coast of Wigtonshire that the best 

 sections of the series can be seen. Here they are 

 recognised resting on the Ardwell group, having at 

 their base "grey and reddish shales, and clays, with 

 calcareous bands and nodules, and enclosed bands of 

 black shale, the lowest members being hard and flaggy." 

 The second member of the Moffat group, as seen on the 

 Wigtonshire coast, consists of black shales with interca- 

 lated clays, like the fire-clays of the coal-measures. Cal- 

 careous nodules and lenticular bands are also associated 

 with the black shales, the whole being so intensely plicated 

 as to render an attempt to determine their thickness 

 extremely difficult. Upon the black shales well-bedded 

 greywacke and gri;s occur with occasional shaly partings. 

 These are succeeded by black shales so much jumbled 

 and jointed, that their thickness cannot be made out. 

 The next sequence consists of grey flagstones, flaggy 

 sandstones, and grits, in beds of varying thickness up to 

 3 or 4 ft., with abundant partings of grey shale. To 

 these succeed a thick band of finely laminated grey shale, 

 3 or 4 ft. Black shales, bands 12 to 18 ft. in thickness, 

 occur next, and the highest members of the group consist 

 of fissile sha'es. 



The Moffat group, as represented in Wigtonshire, has 

 a thickness of about 1,000 ft., of which more than half 

 consists of flaggy greywacke beds. The underlying series, 

 the Ardwell group, probably attains to a much greater 

 thickness. 



The third member of the Upper Llandeilo rocks 

 of the Southern Uplands of Scotland, like the second, 

 derives its name from Dumfriesshire. It is well 

 exhibited in the hill called Oueensberry, and has 

 been designated the Oueensberry grit group. The 

 characters of this third member, as they are seen 

 in Wigtonshire, '' consist of greywacke and grits in 

 massive courses, with occasional bands of grey and 

 greenish shales." Massiveness and regularity of bedding 

 and jointing are the characters of this group. The sand- 

 stones are often coarse ; and sometimes even coarse con- 

 glomerates appear, in which some of the embedded frag- 

 ments are sometimes from 2 ft. to 3 ft. in diameter, a 

 feature which distinguishes the Oueensberry group from 

 all the other members of the Upper Llandeilo rocks of the 

 South of Scotland. Fossils appear to be absent from 

 this group, no trace of them having been met with in 

 the three parallel bands which traverse Wigtonshire. 



In the Dumfriesshire portion of the Upper Llandeilo 

 area of the South of Scotland, there have been recog- 

 nised, above the Oueensberry grit group, black shales 

 with graptolites, the thickness of which have not yet 

 been ascertained. To these black shales the name of 

 Hartfell group has been given. As the typical area 

 where these rocks occur is in the higher part of the Annan- 

 dale district, the sheets of which have not yet been pub- 

 lished, we have at present no account of this group from 

 the Geological Survey. 



The Hartfell group is succeeded by the Daer group, 

 which is made up of hard blue and purplish greywacke, 

 and grey shales. It derives its name from a stream 

 flowing from the north side of Oueensberry into the 

 Clyde. Its strata are greatly folded, and no reliable 

 estimate can be formed of the thickness of the Daer 

 group. 



The Hartfell shales of the Daer group seem to thin 

 out towards the south-west. They have not been dis- 

 tinctly recognised in Wigtonshire, where the Dalveen 

 group, which in Dumfriesshire succeeds the Daer group, 

 is seen resting conformably upon the Oueensberry grits. 



In Dumfriesshire the Dalveen group consists of fine 

 blue and grey greywacke, and shales having no features 

 distinguishing them from other members of the upper 

 Llandeilo rocks. Their estimated thickness is about 

 2,900 ft. They are well exposed in Dalveen Pass, 

 Dumfriesshire, whence their name, and in Dinabid Linn 

 they are seen passing under a coarse pebbly rock, 

 " Haggis Rock." 



In Wigtonshire the lower part of the Dalveen group 

 is seen overlying the Oueensberry rocks south of Corse- 

 well Lighthouse. Here its lower portion is remarkably 

 shaly, but thick masses of greywacke also occur. Among 

 the shaley beds are some bands worked at Cairn Ryan for 

 slates. These slates have long been known as affording 

 graptolites ; and another thin band of black shale also 

 containing the same fossils appears in this group in 

 Wigtonshire. 



In Dumfriesshire above the Dalveen group a scries of 



