1 898.] C97 



RECENT CONTRIBUTIONS TO THE GEOLOGY OF 



IRELAND. 



I —Annual Report of the Geological Survey of the United 

 Kingdom for 1896. By Sir Archibai^d Geikie, F.R.S. London ; 

 1897. Price Sixpence, 



Ouietl}' and steadilj-, with very little recognition, and, unhappil}', 

 with no S3'steni of bringing its publications before the general eye, the 

 Geological Survey goes on its way, unravelling the details of the struc* 

 ture of Ireland, and. effecting the most surprising changes in our 

 knowledge of the country. With a reduced staff, and with w^hat is 

 regarded as only a temporar}- grant, this great scientific duty is carried 

 on ; and it can be said that such work is completed only when our 

 knowledge of the earth itself becomes complete. Already many of the 

 earlier memoirs call for the revision that recent research has shown to 

 be required ; and in the future we may hope for the undertaking of a 

 " drift " survey, representing the actual soils above the " solid " geology, 

 on the same system as that already adopted for the w^hole of England. 

 The simply issued annual reports give one a clear idea of the work 

 accomplished in each year. On pp. 8 to 10 of the present one, we have 

 a summar3- of the areas covered by the four Irish surveyors, and the 

 record of 900 specimens of Ordovician and Silurian fossils added to the 

 public collections by the labours of Mr. Clark, On p. 48, we find the 

 important statement that the Ordovician (Lower Silurian) rocks are now 

 proved to occupy only a small north-western belt, and the tops of a few 

 articlines, in the wide area from the north of Co. Down to Dublin, 

 True Silurian (Upper Silurian) rocks thus receive an enormous extension 

 on our maps, the series represented being mainly Llandovery ; while 

 the epoch of the " Caledonian " folding in Ireland, with its accompany- 

 ing intrusions of granite, becomes placed decisively as post-Silurian, not 

 merely as post-Ordovician, 



The difficult mapping of Co. Mayo is providing at present more prob- 

 lems than can be dealt with. The eruptions south of Lough Mask (p. 49) 

 are now transferred from Llandovery- to Bala times, and are thus con- 

 temporary with those of Snowdon. Mw^eelrea itself (p. 50) is shown to 

 contain both Ordovician and Silurian strata ; while the startling state- 

 ment of the Wenlock age of the Croagh Patrick quartzites receives still 

 further confirmation. The land against which these varied series were 

 laid down was a highland of the old schists — including, we may presume, 

 the quartzite of the Twelve Bens — which la}- to the south of Killary 

 Harbour. The work of 1897 and 1898 wall no doubt give greater preci- 

 sion to the Ordovician boundaries sketched out in the present report. 

 In an}' case, the Ordovician strata in Mweelrea fully prove the con- 

 tention of Sir A. Geikie that the Connemara schists are of much earlier 

 age. For them we must still be content to use the term " Dalradian." 



A 3 



