662 J. A. UDDEN COMPOSITION OP CLASTIC SEDIMENTS 



List of Samples in Table 2 



9. Glacial gravel in a terrace at Bureau, Illinois. 



10. Gravel in the drift on the Government Island, Rock Island, Illinois. 



11. Glacial gravel from near Peoria, Illinois, 



12. Gravel from the glacial drift, Wyanet, Illinois. 



13. Glacial gravel from near Hudson, South Dakota. 



14. Glacial gravel from near Peoria, Illinois. 



15. Glacial sand, Muscatine, Iowa. 



16. Glacial sand from cross-bedded part of a bank, Wyanet, Illinois. 



17. Glacial sand from a terrace, Bureau, Illinois. 



18. Glacial gravel, Peoria, Illinois. 



Materials from single layers of deposits in glacial waters. — Five sam- 

 ples were collected, each from a different single layer in glacial sand or 

 gravel beds. These are as well sorted as some beach sands. Taken to- 

 gether with the other samples from glacial waters, which are poorly 

 sorted, they prove that the currents of the glacial waters were unsteady, 

 sometimes depositing coarse and sometimes fine materials. The coarse 

 admixtures are greatly in excess of the fine admixtures. 



List of Samples in Table 3 



19. Glacial sand from a horizontal single layer, Wyanet, Illinois. 



20. Glacial sand from a single layer in a cross-bedded bank, Wyanet, Illinois. 



21. Glacial sand from an oblique single layer, Wyanet, Illinois. 



22. Glacial sand from a horizontal single layer, Wyanet, Illinois. 



23. Glacial sand from a single layer in a cross-bedded bank, Wyanet, Illinois. 



Terrace materials. — Most terrace materials in Illinois and Iowa are 

 also deposits in glacial waters and show the same characteristics as the 

 latter. Bnt they were deposited at a considerable distance from the 

 continental ice-sheet. 



These materials are also characterized by irregularity of sorting. 

 Samples 34 to 47, inclusive, were taken more or less across bedding 

 planes, so as to represent average conditions for each deposit. Only two 

 samples out of fourteen are fairly well sorted, one being limited to five 

 grades, the other to seven. Sample 35 may be said to have four maxima; 

 samples 34, 38, 45, and 46 have three, and 36 and 47 have two. In 

 averaging the admixtures in such materials it is necessary to select an 

 arbitrary maximum believed to contain materials deposited under some- 

 what similar conditions in all cases. The result shows eight grades of 

 admixtures on either side of the maximum; but the coarse admixtures 

 are nearly twice the size of the fine, the grades farthest removed from 

 the maximum showing the greatest difference in these samples, as was 

 noted in the sands and gravels deposited in other glacial waters. 



