648 REPORT— 1897. 



4. On the Asar of FMand. By P. Kropotkin. 



These observations on the Ssar, or eskers, of Finland were made in 1871. 

 Many researches have been made since by Finnish geologists ; but although the 

 glacial origin of the Ssar is now firmly established, their mode of formation in 

 connection with the ice-sheet still remains uncertain. 



The chief point which appears in regard to the Ssar of Finland and Sweden is 

 that they follow the same lines as were followed by the ice-cap in its southward 

 and south-eastward movement. While taking no heed of important orographical 

 features, they take into account, like glacial striae, minor depressions and eleva- 

 tions, showing that the ice always followed the lines of least resistance. 



The main Swedish &ar descend from the highlands ; they spread next upon an 

 elevMted plain, 100 to 200 feet high ; then they descend to the Malar depression^ 

 cross it. and finally creep over the hilly tracks in the south of Lake Malar. 



At the time of the author's visit to Sweden, the as of Upsala was cut through 

 its whole width at Upsala, for making a new road. It consists of a core, made up 

 of totally unstratified, unwashed, and unsorted gravel, composed of I'ound, angular, 

 and sub-angular stones, from a few inches to several feet in diameter, mixed with 

 sand and finest mud. This gravel is exactly similar to the bottom moraine in the- 

 neighbourhood, only containing a slightly greater proportion of limestone boulders 

 brought from Gefle. This core is covered with a mantle of washed, stratified, and 

 sorted gravels, sands (ripple-marks), and clays, with Baltic shells. 



The Ssar of Finland, represented on an orographic map, all run N.W. to S.E. 

 One of them, the Pungaharju, was described, to show the orographic features of a 

 big Its. The Kangasala 8s, in West Finland, occupies a position which makes of it 

 a sister as to the Swedish S^ar on the western shore of the Gulf of Bothnia. It is 

 a typical as, ninety-five miles long (twenty-two miles explored). It has all the 

 characters of a longitudinal moraine, partly destroyed by the lakes and covered 

 with sands and gravels which were washed by water and were deposited on tlje 

 old shores of a lake which reached a higher level than is now reached by Lake 

 Piijane. The morainic core consists of a typical kross-stensgrus, in which immense 

 scratched boulders are scattered. 



Of later Finnish explorers, Wiik (1876), Gylling (1881), and Lederholm (1889) 

 consider it also as a moraine, modified by water in its superficial layers ; while 

 Berghell (1892) is inclined to consider it as the produce of a glacial river. 



The & of Yvaskylii bears the same character ; while along the Tammerfors- 

 Helsingfors railway the Ss of Ryttila was found to have been largely digged out 

 as a ballast-pit. The washed and sorted gravel was taken away as ballast; but the 

 till (which gives bad ballast owing to its contents of fine glacial mud) was left 

 intact at the bottom, thus showing that the core of the Ss is of morainic origin. 

 The same was observed in the Ss at Dickursby. 



The conclusions to be drawn from these facts, taken out of many others ob- 

 served by the author, are : — A strict distinction must be made between the core of 

 an Ss and its mantla. They are of distinct origin. The latter is always due to 

 the action of water (rivers, lakes, or the sea), while the core, whenever access could 

 be found to it, was invariably of morainic origin. Always it was found to consist 

 of unwashed and unstratified till, and never of fluviatile deposits. This core is 

 often buried under a thick sheet of water-deposits, and occasionally it lies even 

 beneath the level of the surrounding plains. It must have the same origin as the 

 drumlins, horse-backs, cames, &c., which are elongated hillocks formed in the bottom 

 moraine, parallel to the motion of ice, and always accompany Ssar. From the 

 geological survey of Sweden it appears that the bi-asar (small tributaries of the 

 big Ssar) often are such drumlins {kross-asar) ; and while the Rongedala Ss is de- 

 scribed as a ruUsten-as in its lower parts, it is represented as of morainic origin in 

 its upper parts. 



We cannot say yet in which way these morainic ridges were formed, whether 

 under, or within, or on the surface of, the ice-cap ; but the Ssar can safely be taken 

 as longitudinal moraines, superficially modified hy xvater. It is also very possible that 

 the main Swedish Ssar and the Kangasala as were side morainic deposits of the lobes 



