334 MR. J. E. MARE ON LIMESTONE-KNOLLS IN [Aug. 1899, 



the quarry, are marked by intense slickensiding on the bedding- 

 planes, and the joints are also frequently aftected by horizontal 

 slickenside-striations, or striations which were horizontal before 

 the folding of the beds. These slickensides show a crag-and-tail 

 structure like glaciated roches moutonnees, and the reason for 

 this seems to be the same in each case, the rough faces pointing in 

 the direction away from the movement. Variation in the direction 

 of the movement points to the production of the slickensiding 

 before the final folding : that is, to a differential movement 

 of the beds with general parallelism to the bedding. In some 

 cases, here and elsewhere, one set of slickensides has partly 

 effaced preceding slickensides, showing that the movements were 

 not always in the same direction, and probably proving the futility 

 of an attempt (which I had hoped would be useful) to ascertain 

 the general direction of rock-movement by examination of slicken- 

 sided surfaces. 



The matrix of the breccia is in places dolomitized. A microscopic 

 examination of the breccia shows angular fragments of very fossili- 

 ferous limestone set in a granular calcareous matrix. The margins 

 of the limestone-fragments show the suture-like irregularities 

 seen at the junction of the breccia with the lower unbrecciated 

 rock. The sections of the junction between the breccia and the un- 

 brecciated base of the band bring out this suture-like appearance 

 very markedly. The fragments are to a large extent composed of 

 crinoidal limestone, in which the crinoid-remains are seen to be 

 embedded in a compact calcareous matrix. The unbrecciated portion 

 consists of a limestone composed largely of foraminifera in a crys- 

 talline matrix. The foraminifera are in an excellent stafe of 

 preservation, and I believe that we are here dealing with a 

 phenomenon which repeats, upon a small scale, what is seen on a 

 larger one in the knolls, namely the preservation of fossils where 

 there has been relief from pressure, allowing the matrix to be 

 completely re-crystallized. Hence, notwithstanding the present 

 different appearance shown by the limestone-fragments, and the 

 matrix of the unbrecciated portion of the band, I conclude that the 

 two portions of the rock were originally similar, but that the 

 fragments have been practically unaltered by the earth-movements 

 which caused re-crystallization of the original rock at the base of 

 the breccia-band. 



I have taken the breccia as a datum, as it is the thickest and 

 most easily recognizable band in the quarry. I will now proceed 

 to describe the structures presented by the more interesting bands 

 above and below it. 



Some distance above the upper shale, on the left limb of the 

 central syncline (and no doubt elsewhere) is a dark blue calcareous 

 rock : this breaks up along two sets of close-lying subparallel 

 divisional planes, which are roughly at right angles one to another, 

 into rod-like masses. It also splits up along fine divisional planes 

 at right angles to these, and parallel to the bedding, and encloses 

 little lenticles of rock which seem to have been dragged out and 



