Manchester Memoirs, Vol. Ixii. (1918), No. 9. 15 



Plate II. 



Fig. 10. — " Rhyolite " : showing well-defined flow structure which 

 has strongly influenced the form of the deep pitting 

 due to wind-erosion. The under surface is not differ- 

 entiated. 



Fig. 11. — " Syenite " : typical " dreikanter," possibly wholly due 

 to wind-erosion ; showing strong pitting. The under 

 surface also shows erosion. 



Fig. 12. — " Felsite " : the two facets of this pebble are extremely 

 similar and deeply pitted, and both are probably due 

 to wind-erosion. The under surface is flat and water- 

 worn. 



Fig. 13. — Exceedingly fine brecciated and veined sandstone, with 

 the structure brought out in high relief by wind-erosion. 



Fig. 14. — Porphyritic volcanic rock with abundant felspar pheno- 

 crysts : upper surface showing three facets, all deeply 

 pitted and eroded. The pits on the two upper facets 

 (at top in photo) are all elongated in a direction parallel 

 with the ridge between these faces (vertical in photo) ; 

 the pittings on the remaining face show no conspicu- 

 ous elongation. The form of this pebble may, in some 

 part, be due to fracture. 



(All the above figured specimens, and a selection of others from 

 the Wirral locality, have been deposited in the Manchester Museum.) 



