434 STUDIES FOR STUDENTS 



SHALLOW-WATER MARINE DEPOSITS 

 ZONE OF MINOR AGITATION 



There is no great difference between these materials and the 

 still-water lacustrine deposits, though there are differences in dis- 

 tribution, fossils, textural range, texture, etc. The list follows: 



1. Average materials fine in texture. 



2. Rather low textural range (sand to silt and limestone). 



3. Sorted into definite continuous layers. 



Fig. 12. — A section in the Galena dolomite of northwestern Illinois. This is 

 a shallow- water marine deposit in the zone of minor agitation. 



4. Marine fossils. 



5. Distributed continuously over wide areas. 



6. Does not vary greatly in thickness within short distances. 



7. Special markings; ripple-marks (not rill- or wave-marks, or mud- 

 cracks) . 



8. Include chemical and organic deposits. 



9. Bedding planes essentially horizontal. 



This deposit is well illustrated by the Galena dolomite of north- 

 western Illinois, which is shown in Fig. 12. All the essential 



