1858.] HARKNESS JOINTINGS. 87 



Threefold Jointing near Cork. 

 Fossils affected by the Jointing. 

 Age of the Jointings. 

 Cause of the Jointings. 



On the Dolomites. 

 Condition of the Dolomites near Cork. 

 Causes and date of the Dolomitization. 



Jointings in the " Brownstone " and " Yellow Sandstone.'^ — The 

 country around Cork is well marked bj peculiar features, which have 

 resulted from the nature of the sedimentary rock occupying this area, 

 and from certain physical changes which have operated on these 

 rocks subsequent to their deposition. 



The contour of the district exhibits a series of low hiUs generally 

 ranging in nearly an east and west direction ; and these hills are 

 composed of Devonian sandstone. Separating the east and west 

 ranges of hills are valleys ; and in many of them Carboniferous lime- 

 stones are seen, and other rocks appertaining to the lower portion of 

 this formation, — the areas of Carboniferous rocks being the remains 

 of much larger masses which have been removed by denudation. 



The physical features of this district have originated from a suc- 

 cession of rolls, which have affected the strata after the deposition of 

 the Carboniferous series. 



In the deposits which here form both the Devonian and the Carbo- 

 niferous formations there are seen well- developed series of jointings ; 

 these, however, are more extensive, and occur in greater variety, in 

 the limestones of the Carboniferous group. In the Devonian rocks 

 (which consist offine-graineddark-coloured sandstones, well marked 

 by cleavage, and locally called " brownstones " in the lower portion 

 which is here developed, and hght- coloured sandstones, the "yellow 

 sandstones " of the Irish geologists, in their higher parts) the joint- 

 ings in general only manifest one direction, which is nearly I^. and 

 S. ; and these JN^. and S. joints are, for the most part, vertical, and in 

 some instances approximate to each other. The joints pervade both 

 the '^brownstone" and the ''yellow sandstone," but, on the whole, 

 are better developed in the former. They make their appearance 

 wherever the solid rock occurs, and are seen affecting the " yellow 

 sandstones " (which here have greenish strata associated with them) 

 and the higher members of the " brownstones " at Ballefouloo, about 

 a mile west from Monkstown (fig. 1). These N. and S. joints, if 

 we adopt the nomenclature of Prof. Sedgwick, are to be regarded 

 as " dip-joints, ^^ or, in the language of Prof. Phillips, may be termed 

 " master-joints y 



An excellent section, showing the "brownstones" and "yellow 

 sandstones," occurs on the road by the sea-margin between Passage 

 and Monkstown. Here we have the physical features of these de- 

 posits, in the form of cleavage and jointing, well manifested; and 

 there is one feature, of a negative character, as seen in this section, 

 worthy of remark, namely, the absence of any trace of strike-joints 

 where, from the nature of the section, had they occurred, they must 

 have been very apparent. 



