1893.] euideiwe for the Recurrence of Ice Ages. 103 



The stiia3 in question are of various character and depth 

 according to the shape and amount of projection of the mineral 

 point that cut them and the form and texture of the rock attacked. 

 They generally run in straight lines across the stone, as, in glacier 

 movement, changes of direction producing curves such as could be 

 observed on a small area must be rare. They seldom run over the 

 edge further than the protruding mineral could reach while the 

 faces of the stone remained in contact. Separate stones however 

 seem to have not infrequently changed their position, so that a 

 fresh set of striae has been drawn across those first formed. 



The grooves on the solid fioor of rock are therefore apt to be 

 all parallel as seen on the slab of sandstone from near Edinburgh 

 No. 21 or on the piece of Molasse from Lausanne No. 1 ; whereas 

 on loose stones the scratches run in different directions on different 

 faces and cross one another at all angles on the same face as well 

 seen on the large rolled mass of chalk No. 22 from the drift of 

 Roslyn Pit near Ely and on the small boulder of black limestone 

 No. 23 from the great moraine of Lausanne. The striated frag- 

 ment of Silurian No, 24 from the lower boulder clay of Longwathby 

 cutting in the Eden Valley is well scratched on all sides but 

 generally parallel to the longer axis of the stone. No. 25 is from 

 one of the highest patches of boulder clay in the kingdom. I 

 found it at an elevation of 1800 feet on the mountains that bar 

 the southern end of the Eden Valley. It has the grooves and 

 scratches running in the length of the stone and almost all parallel 

 on both sides. 



It must not be supposed that all ice-borne stones will be 

 glaciated. Masses that have fallen on to a glacier and travelled 

 down on its surface to the terminal moraine or even to the sea may 

 never have been subjected to any crushing or grinding. Scratched 

 stones are exceedingly rare on the terminal moraine of any existing 

 Alpine glacier, whereas they are abundant in the drift lower down 

 the valleys. Fragments that show ground and striated faces must 

 have had time to get into or under the glacier, except of course 

 those caught in shore ice of which we are not now speaking. The 

 specimen of Shap Granite No. 26 as it lay in the Eden Valley is 

 therefore interesting in view of the controversies as to the mode of 

 transport of the boulders from Wastdale Crag for it is distinctly 

 ice-worn and thus we know that it travelled, at one time, in or 

 under the ice. 



No. 27 from the drift of the coast of Wexford was evidently 

 caught by sea-borne ice, as it was bored by lithodomous molluscs 

 before it was striated. On it the striae are nearly parallel on the 

 same face but those on one face do not run in the same direction 

 as those on the other. 



