Reviezv^ 



59 



deiuoustrate a series of movements which he ingeniously represents by 

 a diagrammatic curve, the vertical co-ordinate representing the position 

 of the land relative to mean sea-level and the horizontal co-ordinate 

 representing roughly the course of time. The record starts with the 

 land surface elevated 30 feet, at the least, above present sea level, and 

 possibly much more. Tlie chief evidence for this elevation is found in 

 the peat-bed which underlies the estuariue clays in the Belfast section. 



Then followed a period of depression, during which the estuariue clays 

 were deposited, the lower clays in shallow water, say from 10 to 20 feet 

 below present sea-level, and the upper clays of Belfast, according to the 

 evidence of the fauna, in deeper water, supposed to be not less than 

 30 feet in depth. 



These upper clays lie some few feet below present sea-level, but after 

 allowing for this, they appear to denote a laud level that was not less 

 than 25 feet lower than at present, and there is a difficulty on this point 

 which is freely discussed by Mr. Praeger. The difficulty is that the well- 

 marked raised beach shelf which is so well developed aroucd the 

 shores of Belfast Lough indicates a depression of scarcely more than 

 10 or 12 feet ; and it would certainly be most convenient to correlate this 

 raised beach with the upper clays, since there is no trace of a higher 

 sea-niargiu in this quarter, except doubtfully at Ballyholme, where the 

 sand and shingle of the old beach rise higher than usual, but where it is 

 quite possible for a storm-beach to have accumulated somewhat above 

 the general level. If it were not for the deep respect that the geologist 

 habitually feels for the conclusions reached by the workers in other 

 branches of science, he might [venture to ask whether, after all, the 

 fauna of the upper clays could not manage, even if for this occasion only, 

 to dispense with 10 or 15 feet of their overhead water, which cannot 

 surely be so absolutely indispensable to them, provided that they be 

 allowed plenty of congenial mud in which to disport themselves, and 

 that they never be brought above low-tide level I But out of con- 

 sideration for the settled convictions of the conchologist we shall 

 not dare to do more than whisper this deplorable heres}', and will proceed 

 at once to acknowledge that if the evidence for the higher shore-line is 

 lacking at Belfast, it is forthcoming at Larne, where Mr. Praeger is able 

 to correlate the implement-bearing beach-gravels, which are elevated 

 about 20 feet above present high-water mark, with the "deep-water" 

 clays of the Alexandra Dock section. 



After this maximum of depression was reached, there ensued a move- 

 ment of emergence by which the land was brought to its present relative 

 position in regard to the sea, or perhaps slightly above this, as the latest 

 change of all seems to have been a slight sinking back from its highest 

 level of emergence. Mr. Praeger is careful to point out that all these 

 changes might be explained either by postulating alterations in the 

 level of the land, or alterations in the level of the sea ; but that his 

 evidence is distinctly more favourable to the former of these alternatives, 

 since " the impression produced by a rapid survey of the evidence is that 

 these recent slight fluctuations are of an uneven and local character." 



