i^96-l C01.K. — Oldhavim hi America, 255 



The literature relating to the Irish examples was quoted 

 in the first number of the Irish Naturalist (vol. i., p. 13). 

 Although the American specimens do nothing, as Mr. 

 Walcott points out, to advance " the position of Oldhamia in 

 the classification of organic forms," yet the whole question is 

 evidently still an open one; while the absence of the structure 

 from post-Ordovician shales has still to be explained by those 

 who regard it as inorganic. 



CONTRIBUTIONS TO GLACIAIv GKOIvOGY. 



A IVIap to show the distribution of Eskers In Ireland. By 



Prof. W. J. Sollas, l,lv.D., F.R.S. {Sci. Trans. Royal Dublin Society, vol. v., 

 part xiii. Price 2j.) 



In this paper we have another example of that excellent system of 

 publication, by which single memoirs, read before a learned society, 

 are made accessible to the outer world. As a review of the literature of 

 eskers alone, this part of the Transactions of the Royal Dublin Society 

 should be in the hands of most geologists and of all " glacialists." Its title 

 is misleading, for it is far more than a map ; and the map given, by-the- 

 bye, illustrates only a certain part of Ireland. In the north especially, 

 numerous fine eskers exist, which are not set down upon the maps of the 

 Geological Survey, these sheets having been already hachured ; but in 

 the region between Galway and Dublin, Longford and Roscrea, Prof. 

 Sollas has been able to extract the eskers from the unshaded i-inch 

 maps, and from the documents of the Geological Survey, and has 

 brought together a striking picture of their distribution and of their 

 confluence. He sums up his own observations as telling strongly 

 in favour of the subglacial origin of eskers ; the materials of the esker 

 have been accumulated in the lower part of the ice-sheet, and have been 

 left behind when the mass melted away. Hummel, in 1874, suggested 

 that streams running beneath an ice-sheet, or beneath a local glacier, 

 hollow out tunnels, which become choked with sand and gravel ; the 

 eskers are to be regarded as casts of these tunnels. Hoist, two or three 

 years later, held that eskers originated in the gravel washed into the 

 ravines and beds of rivers which were cut in the surface of the ice ; the 

 glacier, on melting, yielded up the drift which it contained at various 

 levels within it, as well as that which lay upon its surface, and this 

 material became arranged along the beds of the streams ; finally, the 

 complete melting of the ice left these river- accumulations in the form 

 of ridges, their sides having been, until then, banked up by the ice. Dr 

 James Geikie adopted the englacial or subglacial view of eskers in 1877, 

 and it is to him that geologists in the British Isles are indebted for an 

 introduction to Hummel's and Hoist's most suggestive papers. Prof. 

 Sollas does justice to other independent workers, such as Winchell and 



