SHAPES OF DRIFT FRAGMENTS. 25 



away. In this maimer the upper surfaces of stones barely projecting above 

 the ground are faceted to nearly a plane, but with more or less of the trem- 

 ulous grooving due to the rhythmical friction of the wind. The grooves 

 are usually a little deeper, as compared with their breadth, when made by 

 the wind than when made by moving water. Sand-carved bowlders are 

 very common in western Maine near the White Mountains, especially on 

 hillsides facing the north and west. Thus certain bowlders of peculiar 

 shape were discovered by Dr. N. T. True at Bethel Village, and were 

 described in 1861 by Prof. C. H. Hitchcock, in a general report upon the 

 geology of Maine. ^ As I have elsewhere stated," these bowlders owe their 

 unusual shapes to sand carving under the action of the wind. Occasionally 

 I have noted sand-carved bowlders in eastern Maine, and many ledges near 

 the seashore are carved with sand by both the wind and the surf The 

 process must be common elsewhere, but it can be recognized only where it 

 is more rapid than the process of weathering. The striae made by wind- 

 blown sand and gravel are usuallj^ invisible, and when best developed are 

 very short, owing to the ready rotation of the flying grains and stones 

 when they strike obliquely against a stone or bowlder. 



Forms scratched, planed, and polished by ice and rocks. (1) By glaclerS. StOUCS Sub- 



jected to attrition by glacier action are said to be glaciated. Many of the 

 glaciated stones show distinct scratches, furrows, or striae. But where, as is 

 often the case in the till, the stones were rubbed by the finer detritus 

 beneath or within the ice, the surfaces received a very fine polish and show 

 no distinct scratches to the unassisted eye. Glaciated stones are often 

 faceted and are almost always vmequally glaciated, some place still retain- 

 ing its original surface or fracture. (2) By icebergs. When icebergs grind 

 off a coast, the underlying rock must be corraded and scratched by any 

 stones that happen to be in the lowest part of the ice and by any sand or 

 other detritus or rock fragments resting on the floor of the sea. The frag- 

 ments would also be scratched and ground. (3) By shore ice, ice floes, and 

 river ice. As shore ice rises and falls with the tide or is m'ged "toward the 

 land by winds and the pressure of ice floes, there must be considerable 

 attrition of the beach pebbles. Floating river ice must also produce a sim- 

 ilar effect, especially when ice gorges have been formed. (4) By landslips. 



' Sixth Annual Report of the Secretary of the Maine Board of Agriculture, pp. 266-267, Augusta, 1861. 

 2Am. Jour. Soi., 3d series, vol. 31, pp. 133-188, Feb., 1886. 



