io The It ish Naturalist. January, 



EARLY GEOLOGICAL MAPPING 

 IN IRELAND. 



BY PROF. GRENVILLE A. J. COLE, F.G.S., M.R.I.A. 



Now that Professor Judd (i) has traced back the foundations 

 of Sir Richard Griffith's geological map of Ireland to the year 

 1 812, a time when the discoveries of William Smith were 

 making themselves generally felt, it is of interest to recall 

 that one of the earliest geological maps of any part of the 

 British Isles was published for the Royal Dublin Society in 

 1802. This is the map drawn up by the Rev. G. Vaughan 

 Sampson, m.r.i.a., to accompany his well-known " Statistical 

 Survey of the County of Londonderry." The work is of course 

 mainly " geognostical," that is to say, it represents, by signs 

 and colours, mineral differences among the rocks, rather than 

 geological horizons. But Smith (2) himself had drawn up his 

 manuscript map of the environs of Bath only three years be- 

 fore, and it is unlikely that the breadth and importance of 

 his work had been realised in 1802 beyond the circle who 

 discussed matters with him in the west of England. The 

 colours used in Sampson's map of Londonderry are reserved 

 for surface-deposits, such as brown for " heath and bog," 

 yellow for " sand," green for " rich loams," &c. But he was 

 fully alive to the desirability of representing the more massive 

 and underlying deposits, which he does by signs scattered 

 over the surface of the uncoloured areas of the map. On 

 Slieve Gallion, in a space of about one square inch, we can 

 thus trace the occurrence of "white lime "(the Chalk), the 

 overlying basalt, and the granite mass stretching to the west. 

 On the fine hills above Dungiven, we see how the Chalk runs 

 as a band under the basalt capping of the range ; while below 

 it comes a band of " marie," where the Triassic beds now 

 appear upon the map of the Geological Survey. No defined 

 boundaries are given to these various formations ; but we are 

 clearly provided with the basis for a true apprehension of the 

 district. The fact that Sampson's main purpose was agricul- 



(i) "The earliest geological maps of Scotland and Ireland," Geological 

 Magazine, 189S. p. 148. 

 (2) See Judd "William Smith's Manuscript Maps," ibid., 1897, p. 439 



