378 Proceedings of the British Association. 



of Ireland, and more particularly to the grey wacke of the county 

 of Down, which, in his opinion, has been there converted into 

 gneiss, mica-slate, greenstone, chlorite-slate, &c, by the action of 

 the adjacent granite. 



Professor Sedgwick noticed the similarity which seems to exist 

 between the fossiliferous grey wacke of Cumberland and Wale?, 

 and a part of the transition series described by Mr Griffith ; and 

 also the resemblance of a portion of what is termed the old red 

 sandstone of Ireland to a part of Mr Murchison's Silurian sys- 

 tem. The phenomena of the magnesian limestone of Ireland 

 seem to the Professor identical with those exhibited in England. 



Mr Murchison pointed out the resemblance of the Pembroke- 

 shire coal district to some of the Irish coal-fields, and also no- 

 ticed, as a striking peculiarity in the geological features of Ire- 

 land, the alternation of the old red sandstone with the mountain 

 limestone, as described by Mr Griffith. There seems in this re- 

 spect a greater analogy to the formations of Scotland than of 

 England. In the latter country the line of demarcation is clear 

 and well marked. 



Captain Portlock, It. E., observed that a closer examination 

 of facts was necessary, before decided conclusions could be drawn 

 on so important a question as that involved in the direction of 

 those currents or forces which had given rise to the accumula- 

 tions of gravel and sand so common on the earth's surface, as 

 well as to the dispersion of larger masses or boulders. In Ire- 

 land, little dependence can be placed on conclusions drawn from 

 fragments of primitive rocks, since the sources from which they 

 have been derived are to be found in such varied positions, 

 Peculiarities of mineral structure may indeed remove this diffi- 

 culty, but it is evident that a very rigid and careful comparison 

 must precede any deduction to be drawn from the position of 

 the removed fragment, and that a perfect knowledge of all ex- 

 isting localities of the parent rocks is equally essential. From 

 fragments of chalk and basalt more decided arguments might be 

 deduced, but in the cases which had been cited, viz. those of 

 Down and Antrim, the distance of the gravel beds from the 

 chalk and basalt cliffs is really so small, that they can only be 

 considered evidence of the direction of a local current, and in- 

 stances are not absolutely wanting of that direction being to the 



