Reviews — Geological Survey of Scotland. 175 



Geologically the area is of considerable interest : it embraces a 

 portion of the Southern Uplands, with rocks ranging in age from 

 Arenig to Ludlow, Old Red Sandstone, and Carboniferous, to say- 

 nothing of Glacial Drifts and more recent deposits. It includes, 

 moreover, various interbedded and intrusive igneous rocks, notably 

 the great granite area of Criffel, with its fringe of metamorphic 

 strata. The map has long been published, for the area was 

 surveyed geologically nearly twenty years ago by Messrs. John 

 Home, D. R. Irvine, and C. R. Campbell, and of these Home alone 

 remains to tell the story of the work. 



The delay in the issue of the descriptive memoir was caused, as 

 we are told by the Director-General, by the publication in 1878 of 

 Prof. Lapworth's classic memoir on " The Moffat Series," a work 

 which rendered it desirable to again examine the area by " the light 

 of his researches, which had at last supplied, in the zonal distribu- 

 tion of the Graptolites, a clue to the unravelling of the complicated 

 structure of the Southern Uplands." This revision has now been 

 accomplished, partly by Mr. Home, partly by Mr. Peach, Mr. 

 Macconochie, and Mr. Teall, with the personal aid of the Director- 

 General. 



The explanation is of far more than local interest, although it is 

 strictly confined to a consideration of the phenomena observed in the 

 district. The subject of contact-nietamorphism does not appear to 

 be dealt with at all fully, the matter being reserved for a promised 

 general Memoir. 



While the elaborate work of Professor Lapworth furnished the 

 key for the interpretation of the complicated stratigraphy of this 

 Palaeozoic region, some considerable additions to our knowledge 

 have been made during the course of the re-examination of the 

 district by the Geological Survey. The existence has been ascertained 

 of lavas, tuffs, and agglomerates in the Arenig group, and also of a 

 well-marked and persistent horizon of Radiolarian cherts and mud- 

 stones in the upper portion of this volcanic series. Although only 

 about 60 or 70 feet thick, these cherts appear to represent the whole 

 succession of deposits which elsewhere in Britain intervene between 

 the Middle Arenig and uppermost Llandeilo strata. 



Interesting nodules composed of oxides of iron and manganese 

 have been found in the Arenig mudstones, and Mr. Teall infers that 

 "the rock was originally a limestone, that it was subsequently 

 changed to a carbonate of manganese and iron, and, finally, that the 

 carbonate was decomposed under oxidizing conditions so as to give 

 rise to the nodular masses of the oxides of manganese and iron." 



The various strata and their fossils, up to the top of the Silurian, 

 are duly noticed, and the igneous rocks are then described. 



The Upper Old Red Sandstone, poorly developed, consists of red 

 sandstone, red clays, and cornstones, which underlie the volcanic 

 group that forms the commencement of the Calciferous Sandstone 

 Series. This Carboniferous group comprises sandstones and shales 

 with marine bands surmounted by coralline limestone. 



The Glacial Drifts are well represented, and proof is given that 



