458 Notices of Memoirs— Prof. E. Eull— 



species, and also by tracks and borings of marine worms. This 

 formation was immediately succeeded by what was called the 

 Lower Silurian, which formed the main tract of the country, ascend- 

 ing the mountains in some instances even to the summit of Lugna- 

 quilla, the core of the range being granite. This granite had been 

 intruded through the Silurian rocks, and, curiously enough, not 

 through the Cambrian rocks, but had aifected the Lower Silurian 

 rocks to such a degree that, from being formed of fossiliferous slates 

 and grits of a darkish grey and brown colour, they had been con- 

 verted into what was called " metamorphic strata," accompanied by 

 the development of certain minerals. Mica had been developed 

 where these rocks came into close proximity. with granite. Granite 

 was, therefore, of a newer date than these Lower Silurian rocks, for 

 otherwise the Lower Silurian would not have been metamorphosed 

 by contact with the granite. The junction was very well seen in 

 numerous places, especially at the foot of Killiney Hill, where the 

 dykes of granite could be seen penetrating the slaty and micaceous 

 schists, also at the remarkable gap, the Scalp, and on ascending 

 Glendalough Valley. The chief limestones were to be found at 

 the chair of Kildare, and on the east coast opposite Lambay Island. 

 These were representatives undoubtedly of the Bala limestone of 

 North Wales, and had yielded a magnificent series of fossils 

 representing the Lower Silurian period. This brought them to 

 the subject of the age of the Dublin and Wicklow mountains ; 

 when they were first elevated ; when they first received their 

 great foldings and contortions, and when the enormous mass of 

 molten matter now constituting granite was first intruded amongst 

 these bodies. To determine this question they had of course to refer 

 to formations newer than the Lower Silurian. At the extremity of 

 the Wicklow and Wexford range they found Old Red Sandstone 

 resting discordantly on the upper edges of the Silurian rocks. There- 

 fore, the Old Eed Sandstone was newer than the period of metamor- 

 phosis, which was the period of the first birth of these mountains. 

 Just as in Scotland, along the flanks of the Grampian Hills, they 

 found the Old Eed Sandstone resting upon the crystalline rocks, 

 which were of the same age as those of the Dublin mountains. Thus 

 they had in both countries similar phenomena. The Silurian rocks 

 were upheaved and converted into land before the Old Eed Sandstone 

 period. He believed the age of the Dublin and Wicklow mountains 

 might be placed at that interval of time which elapsed between the 

 close of the Lower Silurian period and the commencement of the 

 Upper Silurian period. The Old Eed Sandstone was scarcely repre- 

 sented within the area described, except in the neighbourhood at 

 Kiltorcan, on the borders of the counties Wicklow, Wexford, and 

 Carlow. It had, however, yielded some magnificent ferns and other 

 fossil plants which could be seen in the Museum of the College of 

 Science. The next formation was the Carboniferous, which was, 

 perhaps, the most important, extending over the plain north and 

 south, and principally represented in the neighbourhood of Dublin. 

 It consisted of three divisions — lower, middle, and upper. The 



