306 Proceedings of the Royal Irish Academy. 



Dalkey Hills. It is "u-ell and markedly represented by the Scalp, and 

 by tlie Dingle, to the nortli-east of the Scalp. It is, however, -well 

 marked in the llourne ITonntains, as shown by the Survey maps, and 

 faiiiy represents the north-east coast line of Ireland, between Burial 

 Island and Eathlin Island, coinciding with the coast line between 

 Donaghadee and Long E,ock, Co. Down. This joint system is nearly 

 everywhere vertical, and in some places very distinct. Its extension 

 northwards is very remarkable, passing through Iceland, near Hecla, 

 according to a direction which is that of the north-west coast of the 

 great inlet or bay called Hunaflood, or Bear Cub Flood, and which is 

 also that of many of the inlets between Portland and Ingolfshead, 

 on the south-east coast line. It crosses l!v orth "Western America, from 

 Cape Lyon, on the north side, to Mount Fair-weather, on the Pacific 

 side ; passes between Honolulu and TToahoo (Sandwich Islands) ; 

 passes J^Tew Zealand to the east, and nearly parallel to the axes of the 

 islands : through Enderby's Land ; cuts the south coast of Africa at 

 Algoa Bay; traverses Africa, parallel to a line joining the Cape of 

 Good Hope with Cape Lopez Gronsalvez ; cuts the river Congo, at 

 Stanley's Pool, that is, about 0° 30' east of the Kalulu Falls ; passes at 

 Algiers, and, crossing the llediterranean, enters Spain at Tarragona ; 

 crosses the Pyrenees ; passes at Pochelle, St. Malo, Startpoint, Bideford 

 Bay, and the south-west promontory of "Wales. If the line between 

 Beechy Head, in the south, and Cape ^rath, in the north, be taken 

 as about the longest axis of Great Britain, it will be seen that the 

 direction of this axis is about that of the direction under consideration : 

 it will indeed be found to represent sufficiently closely the line joining 

 the coast of Yarmouth with the coast line at Peterhead. It may, 

 therefore, be considered as having a representative character. 



The dii'ection 43° 51' "W. is represented by only short stretches of 

 the eastern Irish coast line, such as the south side of the Bay of 

 Dublin, and the line between Skerries and Balbiiggan. It also cor- 

 responds with portions of the Trap dykes north-east of Lough Erne, 

 with the longer axis of this lough, and with the direction of the Trap 

 dyke marked as running between Magheiy Bay and Trawenagh Bay, 

 Co. Donegal. Outside Ireland, the corresponding Great Circle passes 

 through a number of very interesting points ; but it may be sufficient 

 to remark, that passing thi'ough Monmouthshire, it represents very 

 closely many of the numerous faults characterising the South "Wales 

 coal-field, as may be seen by the Geological Survey of the district. 



The direction 21° 20' E. is represented by parts of the south-east 

 coast of Ireland, the outline of which it goes to form, in combination 

 with the direction 16° 23' E. It also represents the dii'ection of the 

 Downpatrick coast, and the coast line extending between Corsewell 

 Point and Ayr, in Scotland. Furthermore, it may be taken as repre- 

 senting in dii'ection the longer axis of Ireland — that running from 

 Mizen Head to Malin Head, and thus passing through Lough Fergus, 

 on the Shannon, according to its longer axis, and defining the western 

 limit of the middle carboniferous limestone. As a Great Circle direc- 



