ANNIVERSARY ADDRESS OF THE PRESIDENT. xlv 



connected, as usual, with breaks in stratigraphical succession. It 

 was long ago stated, by Sir Henry De la Beche, that the upper 

 sandy and conglomeratic part of the Old Red Sandstone in Wales 

 overlaps, westward, the lower marly portion, or, in other words, 

 that the beds which seem to pass into the Carboniferous rocks over- 

 lap those strata which seem to pass into the Ludlow beds. Though 

 he does not seem to have considered this worthy of mapping, it now, 

 in conjunction with other information, seems to indicate actual un- 

 conformity between the two halves of the Old Eed Sandstone — that 

 is to say, a complete break in succession. 



In the south-west of Ireland a physical break of this kind has 

 been described by Mr. Jukes, where, at the base of the so-called Old 

 Eed Sandstone, from 7000 to 10,000 feet of red beds adhere con- 

 formably, or nearly conformably, to the Ludlow rocks, and from 3000 

 to 4000 feet lie upon these beds as unconformably as it is possible 

 for one set of beds to lie on another, and so pass regularly up into 

 the Carboniferous Limestone. Here, therefore, is an enormous lapse 

 of time, of which there is no stratigraphical representative known 

 in Ireland ; for the Silurian rocks and the unconformable lower por- 

 tion of the so-called Old Eed Sandstone were upheaved and denuded 

 in the most extreme manner before the deposition of the upper part, 

 and neither in fossils nor in physical relations is there any connexion 

 between them. 



In Scotland also there is still more ample evidence of strati- 

 graphical breaks during the deposition of rocks that have all been 

 massed as Old Eed Sandstone. 



In Caithness the lowest beds lie quite unconformably on Silurian 

 gneiss, and therefore the only evidence of anything like the Shropshire 

 beds of passage is derived from the discovery, at Ulbster, of Ptery- 

 yotus in the lower strata under the flags — an important fact, only 

 made known to me two days since by Sir E. I. Murchison. 



In the beds next in the Caithness series (so-called Middle Devo- 

 nian) several of the Fishes are of the same genera with those in the 

 Upper Old Eed Sandstone of Ireland with its Plants and Anoclon ; 

 which division, Mr. Jukes observes, passes conformably into the Car- 

 boniferous Limestone, and, in his opinion, forms the lowest member 

 of the Carboniferous strata. 



Further south, in Forfarshire, it has been shown that the Ptery- 

 gotus-beds (supposed to be beds of passage) again occur, and that 

 these are overlain unconformably by Upper beds of the Old Eed 

 Sandstone. 



But recent investigations by Mr. Geikie show that it is in the Pent- 

 land and Lammermuir hills that the most perfect evidence occurs of 

 breaks in succession. There certain red strata on the horizon of the 

 Pterygotus-beds lie conformably on the highest recognized Ludlow 

 rocks, and these have always, as in Ireland, been massed with the 

 Old Eed Sandstone. On these the red and yellow sandstones, bedded 

 felstones and ashes of the Pentland hills lie in strong unconformity ; 

 and on these again the Upper Old Eed Sandstone strata (Dura Den 

 beds ?) lie in a second strong unconformity, and pass conformably 



