81 



heavals ; one marked by the felspathic nature of the igneous masses 

 affecting the older greywacke;* the other by tlie augitic nature of 

 the trap which has pierced the oki red sandstone and coal-fields, 

 and thrown them into discordant positions. Thus, whilst he indi- 

 cates faults which traverse the whole series, he also demonstrates, 

 that the masses of granite which intrude upon the older felspathic 

 trap, have produced no alteration in the overlying red sandstone ; 

 the latter in fact having been deposited upon those rocks of earlier 

 disturbance, fragments and pebbles of which are included in the red 

 sandstone matrix, and even in the basaltic matter which has been 

 the cause of the second great elevation of the tract. 



This reminds me of an old observation of Professor Sedgwick on 

 the flanks of the Cheviots, where he discovered that the old conglo- 

 merates at the base of the lowest carboniferous strata of Northum- 

 berland are almost made up of Cheviot porphyry ; and that where the 

 coal strata north of Berwick are set on edge, and in one place in- 

 verted, there are dykes and masses of a neAver augitic trap. 



Irish Ordnance Geological Survey — Tabular List of Irish fos- 

 sils. — A compendious volume, entitled ' A Repoi-t on the Geology 

 of Londonderry, and parts of Tyrone and Fermanagh,' has just been 

 published by our associate Captain Portlock, R.E., employed in the 

 Irish Trigonometrical Survey. Illustrated by a geological map, 

 numerous coloured sections, and plates of organic remains, this 

 closely packed volume, of nearly 800 pages, is a sample of how 

 great a mass of matter may be derived fi'om a small district. Not 

 having had sufficient time to study the details of this work, I must 

 crave the author's indulgence if I refer only to such parts of it 

 as have arrested my attention. Captain-Portlock, having some time 

 ago discovered a small patch of Silurian rocks in the region of his of- 

 ficial labours, commenced a careful and systematic inquiry into the 

 nature of the Trilobites with which it seemed to abound, and he 

 now presents us with some very valuable results. In a preliminary 

 discourse he offers many important remarks upon the affinities and 

 anatomy of this group of animals, and after a very elaborate com- 

 parison of all the forms which he could detect in his district with 

 those published by British and foreign authors, citing among the 

 latter several works very little known to us, he arrives at the con- 

 clusion, that of sixty species in this palaeozoic tract, fifty-two belong 

 to true Silurian strata (for the greater part Lower Silurian), and 

 eight only to the enormously developed carboniferous limestone of 

 the North of Ireland. This fact is quite in accordance with what 

 has long been my belief, that the Silurian or oldest palaeozoic group 

 is the great centre of Trilobitic life. Describing many ncM' forms, 

 which are figured, he establishes several new genera, among which 

 the Rhemopleurides, obtained from the Lower Silurian rocks, is a 

 very curious and apparently quite distinct trilobite. There are 

 but small traces of Upper Silurian or Devonian deposits in this 

 district, the greater part of it being covered by a carboniferous 

 series, consisting, as the mountain limestone of Ireland is known 

 to do, of much sandstone and slate as well as limestone. Find- 



