MONIAN BYSTEM OF KOCKS. 535 



as part of the series. These latter are the most importaut for 

 connecting the two areas ; for after becoming tolerably familiar 

 with the South- Stack series, but not expecting to find them again 

 on the opposite side of the Channel, I was immediately struck with 

 their resemblance to those at Howth, when I visited the latter in 

 the company of Prof. Sollas. In the northern part of the promontory 

 there is a good coast-section, showing slates and grits of very meta- 

 morphosed character. They are highly cleaved, which somewhat 

 obscures their bedding inland ; but the beds are obvious on inspec- 

 tion of the cliffs, where they show the same contortions and general 

 succession as at South Stack. The sericitic slates that come on near 

 the lighthouse are exactly matched in Holyhead Island ; and further 

 south, in j^eedles Bay, are found the same kind of bedded earthy 

 rocks as we find at Porth-y-grug, each bed being only 3 or 4 inches 

 thick and showing a hardened capping, and entirely without meta- 

 morphism. Again, there are the large masses of quartzite, which 

 occur in a very irregular manner, and which seem to have no bedding 

 in themselves, but to interfere with the regularity of the others. 

 These are certainly somewhat different from most of those in 

 Anglesey; they are too large to be thought to be quartz-knobs, 

 and though we might compare them with the Holyhead quartzite, 

 they are not followed by chloritic schists. On the other hand the 

 quartzites of Roscolyn are bedded rocks, and the only masses in 

 Anglesey to compare them with are those which stand out from the 

 surface near South Stack itself. But whether they can be exactly 

 matched or not, it is in Anglesey, and there alone in England, that 

 we must look for phenomena of this kind at all. All these points, 

 in which the Howth beds resemble the South-Stack series and not 

 any true Cambrian rocks, lead to the conclusion that they are the 

 continuation of the former across the Channel. 



But this correlation leads us a step further. The rocks of 

 Howth, though in some respects very distinct from those of Bray 

 Head, are yet linked to them so closely by position and by 

 general character that we cannot separate them widely. The 

 latter differ in being more closely bedded, the beds being grits of 

 a few feet in thickness and alternating with more slaty rocks ; 

 they are not cleaved, therein resembling the less altered or 

 more earthy rocks of Howth. They contain much chlorite, and 

 towards the south thinner and more slaty beds come in, and the 

 slate-rocks on Carrickgologan are very similar to those of Howth. 

 Above all, there are the same great quartz-masses ; these seem, at 

 Bray Head, to cat completely across the bedding, a fact which is 

 represented on the map by a fault, of which I could find no further 

 evidence. The mass of Carrickgologan in the same way comes in 

 in defiance of stratigraphy. In certain parts its rocks show banding, 

 but these furnish no assistance, as the rocks if disposed according to 

 such bands must be faulted on all sides. I have not been able to 

 make out the true nature of these quartz-masses as yet ; but what- 

 ever they are, they are again a great bond of union between these 

 rocks and those of Anglesey. These rocks have been called Cambrian, 



