JRevieus — The Survey Memoir on the Scottish Uplands. 475 



geological facts and phenomena, needing for their explanation and 

 classification a new race, so to speak, of unexpected geological 

 conclusions and principles, destined to play an important part in the 

 future of British geology. 



In their original mapping of the Uplands, between 1854 and 1873, 

 the officers of the Survey followed the familiar formational or regional 

 ])lan of working out the succession, classing each broad geographical 

 belt of strata having as a whole special and characteristic lithological 

 features as the outcrop of a distinct rock group or formation, fixing 

 its relative place in the general series of such formations by its 

 visible superposition, and its approximate geological age by its 

 collective fauna ; a method which had proved itself in every case 

 fully adequate for the ascertainment of the true sequence among the 

 Lowland formations of Britain, and even among the tilted Silurian 

 rocks of Wales, the North of England, Lanarkshire, and the Pentlands. 

 Combining the work of all their predecessors with the results of 

 their own researches, and interpreting the whole in this way, they 

 concluded that the strata of the Uplands dipped off a grand anti- 

 clinal form ranging from Dumfries to St. Abbs, and that its highest 

 formation, the geological age of which was fixed by its Caradoc 

 fossils, lay in the lap of a synclinal form running through the 

 Leadhills to the Moorfoots. Between the anticlinal line and the 

 synclinal form occurred a series of seven rock-groups or sub- 

 formations : (1) the axial or Ardwell beds, (2) the Moffat Black 

 Shales, (3) the Queensberry Grits, (4) the Dalveen Group, (5) the 

 Lowther Shales, (6) the Leadhills Black Shales, and (7) the 

 Carsphairn Grit Group. These were all classed as being of 

 Llandeilo age, for most of them afforded certain well-known 

 Llandeilo graptolites. It was true the strata were often so folded 

 that it was impossible to say whether we were ascending or 

 descending in the order of the beds, but the general sequence 

 appeared evident enough. It was true that with the Llandeilo 

 graptolites were often intermixed forms known in so - called 

 Caradoc and higher strata in other parts of Britain, but the well- 

 known and generally accepted Theory of Colonies of the illustrious 

 Barrande was supposed by many to afford a very simple and 

 natural explanation of such anomalies. 



But the facts ascertained and the results arrived at stage by stage 

 by myself and others in the geology of this Upland region, more 

 especially in the Moffat and Girvan districts (1872-1882), made 

 it evident that the regional or formational plan of mapping these 

 convoluted rocks of the Uplands was unreliable, and that the only 

 method found invariably trustworthy was that of working by means 

 of palseontological and lithological 'zones.' The host of evidences 

 accumulated during the same period by geologists and pal asontolo gists 

 in Britain, Scandinavia, France, America, etc., that the Silurian 

 Graptolite was as capable as the Jurassic Ammonite of being 

 employed as a stratigraphical index, made it equally plain that the 

 true sequence of the Silurian strata from end to end of the Uplands 

 must of necessity be that of their zones of graptolites. 



