126 J. T. Jut son: 



iibly nut more tliaii 18 in. tJiick as a riik, of fine and coarse 

 ■detritus. 



The occasional streams that traverse the lowlands b-ecome diffused 

 and rapidy die out ; they have not carried down the whole of the 

 •deti-itus. Probably most of such detritus has been transported by 

 the slow drifting action of rain actin<j: on the fine material, and by 

 the slow gravitational drift of the coarser material. 



As the detritus slowly travels down the slopes of the lowlands, 

 much of the fine material is removed by wind and rain, and hence 

 loose sands begin to accumulate, and are built by the wind into 

 .miniature ridges. Consequently, the bed-rock becomes exposed and 

 .surface drainage becomes. more concentrated. Thus there is a dis- 

 tinct change from the detritus-covered slope, with practically no 

 distinct water channels to the miniature sand ridges and rock- 

 floored channels between. The miniature ridges grow into regular 

 ;sand ridges, and the small channels grow into the largely rock- 

 floored arms of the lake. In the area of the miniature ridges, and 

 of the irregular sand ridges, water, once it is concentrated in 

 •definite channels owing to wind action, must remove some mate- 

 rials; but water action must almost fail in the more eastward areas, 

 where the regular sand ridges occur, the rock-floored channels be- 

 <!ome pronounced arms, and the surface becomes lower ; although 

 portion of the (piartz detritus that rests on the floors of the arms 

 is probably carried there by rushes of water. 



It therefore seems to the writer that the wind is mainly respon- 

 rsible for the arms as well as for the sand ridges, inasmuch as the 

 wind apparently blows the detritus from the arm areas on to the 

 parallel sand ridges, and in doing so, exposes the bed rocks, which 

 in turn must be corraded to some extent by the blown sand as well 

 :as further disintegrated by ordinary weathering, the products of 

 such weathering being carried away by the wind. 



It might \)e> argued that the longitudinal sand ridges are merely 

 llie remains of a one-extensive continuous sand-covered aiea, wliich 

 lias been eroded either by wind or water so as to form the lake 

 arms. The sand of the I'idges can, however, in any case, be 

 explained only as wind-borne, and on the " lowlands " there are 

 few sand ridges, such ridges l)eing, in the area referred to, almost 

 always associated with rock floors, so tliat the above supposition 

 Avould not apparently hold good. 



The dominant winds appear tf) l)e westerly. The sand ridges 

 and lake arms are therefore approximately parallel to such direc- 

 tion and. tlie ridges are longitudinal ones, with bare troughs 



