490'. 



SCIENCE. 



[N. S. Vol. VII. No. 171. 



pools. It is about 500 feet in diameter and 

 60 feet deep, its surface lying 160 feet be- 

 neath the adjacent upland. Steep clifiFs rise 

 on three sides, while the gorge opens east- 

 ward to Batternut valley. All the features 

 of a dry Niagara are here disclosed in great 

 detail. Several excellent illustrations ac- 

 company the paper. 



ESKERS IN IRELAND. 



' A MAP to show the distribution of eskers 

 in Ireland,' by W. J. Sollas (Sei. Trans. 

 Koy. Dublin Soc, V., 1896, 785-822, maps), 

 is a serviceable summary, based chiefly on 

 the work of the ofScial Geological Survey, 

 with personal observations in certain dis- 

 tricts. Although predisposed in favor of 

 the marine origin of askers, the author 

 concludes that nothing is so competent to 

 explain their various features as the action 

 of streams in subglacial tunnels. Their 

 height is 50-60 feet ; their elevation above 

 sea-level seldom reaches 400 feet. The 

 convergence of branch eskers towards a 

 trunk is properly regarded as one of the 

 most indisputable signs of stream origin. 

 Three notably fine esker systems deserve 

 mention ; the Midlands sj'stem, on the 

 central plain, half way from Dublin to the 

 west coast, where three distinct and many 

 subordinate eskers converge eastward ; the 

 Ballyhaunis system, with three distinct 

 branches converging northward against the 

 general slope of the country between the 

 headwaters of the south-flowing rivers 

 Suck and Clare ; and the Portumna system, 

 having three branches converging eastward 

 with the general slope of the country from 

 Slieve Aughty into the valley of the Shan- 

 non above Lough Derg, but crossing the 

 subordinate valley of the Ardultagh on the 

 way. One member of the Midlands system 

 near Athlone is illustrated by a special 

 map, showing it to be of exceptional irregu- 

 larity of form, a confused network of ridges 

 with disordered structure, instead of a long 



narrow ridge ; here, if anywhere, an origin 

 in a super- or englacial stream might be in- 

 ferred. A useful summary of previous 

 writings is included in the essay. 



DESERT CONDITIONS IN BRITAIN. 



The interpretation of the past through 

 the present is a canon of orthodox geology. 

 Under its guidance, the existing oceans and 

 rivers have been carefully studied ; but the 

 deserts of to-day have until recently re- 

 ceived little consideration as the repre- 

 sentatives of ancient conditions. An oppor- 

 tune article on ' Desert Conditions ia 

 Britain,' by J. G. Goodchild, (Trans. Edin- 

 burgh Geol. Soc, VII., 1899, 203-222), 

 calls attention, first, to the characteristic 

 features of existing deserts, by which their 

 former occurrence may be recognized ; 

 second, to the probability that the Britisli 

 Isles have more than once had a desert 

 climate in the remote past. Various de- 

 tails are given concerning the composition 

 and structure of the deposits of deserts. 

 For example, comparison of desert and sea- 

 shore sands shows that any sandstone 

 largely composed of well-rounded grains 

 was probably formed under arid con- 

 ditions on a land surface. The British 

 deposits of Triassic, Devonian and Torri- 

 donian times are thought to have beea 

 formed under inland, desert, continental 

 conditions. 



The change thus implied in continental 

 outlines needs consideration along with the 

 arguments commonly quoted in support of 

 the permanence of continents. Great 

 Britain must have had much land or a high 

 mountain range to the windward when the 

 desert sandstones and saline deposits of 

 Cheshire resembled the ' salinas ' of modern 

 deserts. Otherwise the earth's axis must 

 have shifted ; for the low western border 

 of a continent in mid-temperate latitudes 

 is the last place in the world where salinas- 

 and desert sandstones can form. 



