1852.] HARKNESS SILURIAN ROCKS OF SCOTLAND. 395 



bands of Dumfriesshire, described in detail in bis former memoir, 

 through the greater part of Selkirk to the neighbourhood of Gala- 

 shiels ; and he considers that the opinion he formerly offered on the 

 probable repetition of the anthracitic bands and their accompanying 

 greywacke beds by means of faults * has been confirmed by his sub- 

 sequent observations. In calculating the thickness of the formation, 

 the author takes the area included between the most northerly band 

 of anthracite at Greskin, about four miles north of Beatock, and the 

 black shales at Elvanfoot that lie below the conglomerate on which 

 the Wrae limestone reposes, as comprising the great bulk of the 

 strata which make up the series. The distance between these two 

 points is six miles across the strike, for which distance the dip is on 

 an average 70° to the N.N.W. From these data Mr. Harkness gets 

 a thickness of about 24,000 feet, and, estimating the above-men- 

 tioned conglomerate and the deposits about Girvan, together with the 

 lowest greywacke sandstones next the syenite, at about 6000 feet, he 

 gets a total thickness of about 30,000 feet for the Lower Silurian 

 rocks in the south of Scotland ; an estimate not greatly differing from 

 that of Professor Nicolf . 



With regard to the fossils, — in addition to those mentioned by the 

 author in his former communication, he has found in the shales con- 

 nected with the anthracite- bands Diplograpsus teretiusculuSy Rising., 

 and J), ramosus. Hall ; the former at Glenkiln, the latter at Hart- 

 fell, Dumfriesshire :{:. 



In these graptolite-shales he has in vain sought for the Graptolites 

 priodon {—G. ludensis^ Murchison), first quoted by Professor Nicol 

 from the Grieston slate, and above or below which bed it has not 

 yet been found in Scotland. It does not occur in any of the strata 

 further south, unless it be at Balmae, Kirkcudbrightshire, associated 

 with a new species, the G. Flemingii, Salter, and numerous "Wenlock 

 fossils. Mr. Harkness remarks too on the occurrence in the black 

 shales of Loch Ryan of several species of Graptolites which are 

 equally characteristic of the anthracitic shales of Dumfriesshire, sup- 

 posed by him to occupy a very much lower horizon. 



Finally, in the coloured shales of Benbuic, Dumfriesshire, and the 

 similar beds at Barlae, Kirkcudbrightshire, the author has detected 

 Annelids and Fucoids {Nereites and Pal(jeochorda). 



Mr. Harkness no longer refers these Silurian rocks of Dumfries- 

 shire to the Caradoc age, as in his former memoir, but he believes 

 them to lie below the representatives of the Llandeilo flags, as sug- 

 gested by Sir R. I. Murchison § ; and the whole evidence goes to 

 show that some of the rocks of the south of Scotland lie very far 

 down in the Lower Palseozoic series, occupying a position equivalent 

 to the Skiddaw slate described by Prof. Sedgwick. 



* Loc. cit. p. 51. t Quart. Journ. Geol. Soc. vol. vii. p. 58. 



X See Mr. Salter's observations on the Graptolites of the South of Scotland, 

 supra, p. 388. 



§ Quart. Journ. Geol. Soc. vol. vii. p. 162. 



