Vol. 62.] CARBONIFEROUS ROCKS AT RUSH. 281 



reaching which place they are seen to pass upwards into the Rush 

 Conglomerates. The strike of the rocks on the southern shore (see 

 fig. 2, p. 280) forms a sigmoidal curve, and the beds are arranged 

 in an elliptical basin followed on the north by an elliptical dome, 

 the long axis of the basin running in an approximately east- 

 and-west direction and having an easterly pitch. The principal 

 axis of the folding corresponds with the strike of the cleavage. 



At the western end of the outcrop, in the neighbourhood of the 

 well called Tob berkilleen, and at a horizon about 200 feet 

 above the lowest visible bed, there is a band of limestone [II 1 1>~\ 1 

 containing a few fossils. It sometimes stands out from the 

 neighbouring slates in small dome-like elevations, and can be traced 

 as a broken and twisted band for some distance, until it becomes 

 lost in a mass of nodules which seem to be the result of the 

 disintegration of the limestone by the forces that produced the 

 cleavage. A second well-defined limestone-band [R4«] occurs 

 some 150 feet above the first, and a third [R 6 6] is found about 

 250 feet above the second. Their peculiar outcrop will be described 

 later. 



These lower beds of the Rush Slates (that is, up to the third lime- 

 stone-band R 6 h) have a curved strike and a rather low dip, usually 

 from 10° to 20°. They form a low rocky shore, almost wholly 

 below high-water mark, the argillaceous slates having a rather 

 smooth aspect, while the more calcareous zones weather with ragged 

 edges. To make out their general structure is an easy task ; but 

 the details give much more trouble, owing to the frequent obscura- 

 tion of the bedding by cleavage, to the growths of seaweed on the 

 rocks, and to the monotonous character of the beds themselves. 

 Several fault-lines can, however, be traced in the slates ; but the 

 fractures all appear to have a very slight throw, and do not affect 

 the genera] stratigraphy. 



Xear the third limestone [R 6 b~\ the coast-line changes in 

 direction, and turns northward. This change is accompanied by a 

 rapid increase in the dip of the beds up to 60° or 65°, and at the 

 same time the curved strike straightens out so that the beds run very 

 regularly in an east-and-west direction. This change in strike is 

 naturally accompanied by some displacement of the beds, and 

 accordingly a number of sub-parallel faults, with some connecting 

 fractures, can be seen here running in a direction a little to the 

 north of north-cast; but their throw is insignificant, varying from 

 a few inches to a few feet. A large nest of calcite, on the shore 

 near high-water mark, marks the intersection of two of these faults. 

 The strike of the beds is now at right-angles to the coast-line, and 

 the scenic effect here is quite different from that of the beds on the 

 southern shore. The rocks now present a series of sharp ridges 

 running out to sea, steeply inclined on the northern or dip-face, and 

 but slightly broken by the small cross-faults just mentioned. The 

 ridges are separated from each other by sharply-defined gullies, where 



1 The notation R 1 b, R4o, etc. refers to the horizons as shown in the 

 vertical and horizontal sections, and catalogued in the faunal lists. 



