Reviews — Vrof. HuWs Physical Geology of Ireland. 127 



beaches, river terraces, etc., which are so numeroTis and widely spread. The author 

 still adopts the same classification as he formerly did, of these representatives of 

 '' The Great Ice Age," and makes three groups. (1) The Lower Boulder-clay or 

 Till ; (2) Middle Sands and gravels, the Limestone gravels of Ireland ; and (3) the 

 Upper Boulder-clay, and notices in some detail the peculiar circumstances under 

 which each of these occur. It will be sufficient here to indicate the conclusions, 

 that the earlier period indicates a time when the surface of the country was more 

 elevated than now, but was somewhat in the same condition as the north of Green- 

 land, etc., is at present, that is, was covered with a continuous ice-sheet of great 

 thickness, and in continued motion in given directions. Secondly, a period of com- 

 parative depression, amounting probably to 1500 feet, accompanied by an ameliora- 

 tion of climate, and an overspreading of the land by the ocean, when water-arranged 

 deposits of sands, gravels, etc. (often containing shells), were formed; and thirdly, a 

 period of gradual elevation, when glaciers again accumulated in local centres around 

 the higher grounds which produced the true glacier moraines, still so frequent in the 

 highlands of the country, and from which drifting icebergs probably conveyed, and 

 dropped at intervals over the country, the boulders which are now found resting on 

 the Middle Sands in many places. It is, however, but right to notice the fact that 

 this classification, although adopted by many, and now before geologists for many 

 years, has by no means commanded universal acceptation. There are still many who 

 hold that the subdivisions noticed are merely local, and by no means so general as to 

 afi'ord sufficient data for the large and wide generalizations which have been based on 

 them. Our author does not himself accept some of the views of other glacialists. 

 We find in his pages no evidence of a belief in the second outspreading or return of 

 a great ice-sheet, after the formation of the Middle Sands, although this is the view 

 of others, and he has been careful to explain fully the much more limited extent, 

 and frequent total absence of the Upper Boulder-clay. The Lower Boulder-clay is 

 by far the most widely distributed of the three groups, occurring in greatest mass in 

 the lower grounds and deeper valleys. Most of these valleys have, in fact, been re- 

 excavated out of it, detached patches of it being left on the side slopes. But even 

 this lower division is not universally present, and even in the lower grounds there 

 are instances where considerable areas are entirely free from it, while closely ad- 

 joining areas are thickly covered. The Upper Boulder-clay, on the contrary, is much 

 more sparingly distributed, and in many parts of the country it has never been 

 deposited. It further often shows distinct signs of arrangement in layers or strata, 

 and has therefore been formed or rearranged by water, while the gravels and sands, 

 on which it is said to rest, give evidence of erosion by water action, but do not 

 appear to have been fairly groimd down, or displaced by a mass of ice. The upper 

 limits of this deposit appear to be less than 1 000 feet above the present sea-level. 



Then we have a series of terraces in the highlands which are attributed to succes- 

 sive formation along shores as the land was emerging from its depression during the 

 Middle Glacial period, at a time when the land was gaining on the sea, and when 

 pauses in the upward movement took place. The " Eskers " are noticed as " the 

 results of tidal and other currents acting on the soft materials of the drift, as thev 

 oscillated within narrow channels, bounded by the ridges of the unsubmerged land, 

 piling them up along tortuous lines in the form of embankments" (p. 99). Mr. 

 Kinahan's distinctions of Bar-eskers and Shoal-eskers are alluded to. There is then 

 a full notice of Local Moraines, or true Glacier Moraines, both lateral and terminal, 

 and numerous instances given both from the Wicklow and the Galway Mountains. 

 "We then pass to Baised Beaches and Eiver Terraces ; and the evidences of the suc- 

 cessive steps in the elevation of the land to its present level are brought down to the 

 " lofoot beach," which is traced along the coast from the north to Dublin, where it is 

 shown probably to merge into the old estuary terrace of the river Liffey, on the flat 

 surface of which some of the principal parts of the capital of Ireland are built 

 (Custom House, Post-office, Sackville Street, Bank of Ireland, University, etc.). In 

 this terrace, with the shells have been found fiint implements, establishing the fact 

 that it has been formed since the occupation of the country by its early inhabitants. 

 This, therefore, connects the Geological with the more purely Archaeological portion 

 of the history. A capital little sketch geological map, coloured by hand, forms the 

 frontispiece to the book, and to those who have not at hand any larger or more 

 detailed map, it will give a fair clue to the general distribution of the various rocks. 

 ( To he concluded in our next Number.) 



