126 Revieivs — Frof. HiiWs Physical Geology of Ireland. 



After a brief notice of the frequent occurrence of basaltic dykes in tbe country 

 adjoining these volcanic rocks, the author proceeds to the only known Pliocene 

 beds in Ireland. These occur as quietly deposited beds of clays, filling in a part of 

 the older extent of Lough Neagh. They now extend 80 to 90 feet above the level 

 of the lake, and have been pierced to a depth of 300 feet, the maximum thickness 

 being nearly 600 feet. They rest on an eroded surface of the Miocene basalt, from 

 which they are separated by a bed of rude conglomerate formed by masses of these 

 basaltic rocks. 'Ihey are generally stiff and plastic bluish clays, much used for 

 coarse pottery, etc. In them remauis of what is described as an tfnio ' have been 

 found, and also of plants— the whole character of the beds indicating a quiet 

 deposition under tranquil waters in an equable if not a warm climate. They were 

 the old lacustrine delta deposits of the Upper Bann and other streams entering 

 Lough Neagh from the south. The PUocene period is but sparingly represented in 

 any part of the British Islands, and these deposits become of even greater interest 

 from the absence of any contemporaries. Of the Pliocene period in Ireland, Prof. 

 HuU says, "Ere it set in, the volanic fires had smouldered away. It was an age of 

 calm repose, separating the period of volcanic activity on the one side from that of 

 frost and ice on the other ; and during its continuance the ordinary agents of 

 denudation— rain, rivers, and sea waves — carried on their operations without unusual 

 interruption, but with marked effect in modifying the physical featui-es of the north 

 and adjoining districts of Ireland." (p. 76.) 



This brings us to the close of the Tertiary period. There still remains, however, 

 a long series of deposits to be noticed, which in reality cover more than three-fourths 

 of the whole area of the country, and to the presence or absence of which a very 

 large amount of the varying characters of its scenery is due. Important, however, 

 as they are, we cannot afford space for more than the briefest notice of these " Post- 

 Pliocene or Drift-deposits," as Prof. Hull classifies them, — the Glacial and post- 

 Glacial clays, sands, gravels, etc., and the still more recent deposits, forming raised 



has in its progress enveloped. Many, but not all, the flints are changed to red, and 

 the chalk fragments are comparatively few, the lime having, it is probable, contri- 

 buted to form the enveloping paste, which is in part rotten and soapy. Some of the 

 immersed fragments of chalk are powdery to the touch, though still retaining a 

 definite form, and such is also the case with the flints. The great body of the trap 

 is here concretionary ; and as the softer portions wear away, the harder projecting 

 lumps look like huge boulders in a rude conglomerate. The bottom portion is 

 obscured by rubbish, so that it is impossible to say whether the trap has risen 

 through the gap, as through a crater, or has been poured into it from above, but on 

 the east side the chalk in a considerable mass rests upon trap, and is at the same 

 time overlaid by it." Now let him turn to Jukes's Manual of Geology, edited by A. 

 Geikie, 3rd edit., 1872, and at p. 271 he will find a figure (fig. 107) intended to re- 

 present the facts seen at the same locality exactly — from a sketch made by Prof. 

 Geikie himself. After noticing where this assumed ' neck ' occurs, he says : " A 

 cavity, measuring about fifty yards across at the top, has been blown through the 

 chalk, and also through a previously erupted sheet of basalt, and this cavity, after, 

 perhaps, serving as an orifice for the discharge of some of the tufi's of the district, 

 was finally filled up with a coarse mass of rubbish, consisting of blocks of basalt, 

 chalk, etc., imbedded in a dirty green gritty trappean paste." The writer thinks it 

 evidently quite beneath his consideration to think of giving any proofs of these boldly- 

 asserted views — or to offer the slightest explanation of how his ' gritty trappean 

 paste ' was formed, or when. Then as the last step in the history of this curious 

 case, we have Prof. Hull (p. 56) saying: "The old necks are choked up by 

 bombs which have been blown into the air, and in falling back have filled up the 

 throat," referring to this very case, near Portrush, and then (on p. 70) he withdraws 

 from this view, and holds these cases to be old pipes in the chalk, " into which the 

 basaltic masses have fallen or slipped down," that is, we presume, after they had 

 been to a considerable extent at least, if not entirely, cooled and hardened. Has he 

 any proof of this ? If so, why is it not noticed ? After the student has traced the 

 successive steps in the history of this sketch, and seen the several additions in the 

 story, which each of its narrators have added — additions for which they were indebted 

 purely to their own poetic imaginations — we cannot help thinking that, so far as any 

 real truth, objective truth, is concerned, he will return to the description of thirty 

 years since, where he finds the limits of knowledge and ignorance clearly noted and 

 candidly avowed, in preference to the apparently more finished, perhaps, but less 

 thorougly established dogmas of recent observers. 

 ' See Geol. Mag. Dec. 1876, p. 557. 



