Dr. C. Callaivay — On Comparative Lithology. 263 



in the microscope to Prof, Bonney as " schist of late type or perhaps 

 only schistose .... fragmental structure still conspicuous." 



4. Similar schistose rocks, more highly mineralized. 



5. Quartzite (South of Carrick Bridge), with thin seams of soft 

 grey or whitish schist. 



The dips of the above are at 40°— 65° to N.N.W. 



At Bannow Bay, we are towards the western end of the same 

 band. East of the Baj?^, the rocks are grey shales (Ordovician) and 

 light-green and purple clay-slates (Cambrian) ; but east of Bally- 

 madder Point, Pebidian rocks are well exposed. Grey and greenish 

 schistose slates of the type prevailing N.W. of Wexford occur. A 

 variegated green and white variety is beautifully contorted. We 

 have also some hornstone-like slates and laminated hornstone. 



The Pebidian rocks of the Southern Zone are well seen in a 

 traverse from Ballycogly to Tom Haggard. The rocks are tolerably 

 uniform from end to end, consisting typically of pale-green altered 

 slates, with some gritty bands. The mineralization is not so great 

 as in the Northern Zone. The strike is to the W.S.W., and the dips 

 northerly at 50° — 85°. I saw no qnartzites here. 



North-west of Greenore Point, there is an outcrop of the ordinary 

 altered slates or shales, and a band of fine-grained crystalline 

 limestone. At the Point is a rock which Prof. Bonney thinks is 

 " probably an andesitic lava." 



In the Hill of Howth and near Aughrim the evidence for a 

 Pebidian age is, so far as I know, purely lithological. In these 

 localities, it may be objected that I am the victim of hand-specimens. 

 But if the rocks are not Pebidian, what are they ? No one has 

 proved that they contain Cambrian or Silurian fossils ; and they do 

 not form part of any known Palaeozoic formation. We are thus 

 driven back upon comparative lithology. If we reject this test, we 

 are left in utter darkness. In Anglesey and south of Wexford, we 

 fortunately possess stratigraphical evidence of Pre-Cambrian age, 

 which in northern Leinster appears to be wanting ; but since the 

 rocks of Howth and Aughrim are quite unlike anything we know of 

 Cambrian or Silurian age, while they display a marked resemblance 

 to the Anglesey and Wexford Pebidian, both in mineral characters 

 and state of crystallization, I hold that I am fairly justified in 

 referring them to the Pebidian system. At the very least, I have a 

 right to challenge those who call them altered Cambrian or Silurian 

 to offer evidence for their contention. 



When we pass to Ulster, we find a group of strata which I have 

 called the Zoiigh Foyle Series} The lithological resemblance 

 between these rocks and the Pebidians of Leinster and Anglesey is 

 very marked. Quartzites, quartzose grits, foliated grit, schistose 

 shales and slates, schists with distinct clastic structure, and black 

 phyllites or subcrystalline schists, are the chief types. This is not a 

 case of similarity between two Icinds of rocks, but between two 

 assemblages of rocks. We have in Ulster a group mainly composed 

 of six or eight varieties, and in Leinster is found a group chiefly 

 1 Quart. Journ. Geol. Soc. May, 1885, p. 22. 



