Raymonp.— Correlation of the Ordovician Strata. 
Fig. 1. 
Fig. 2. 
Fig. 3. 
PLATE 6. 
Thin section of glauconitic limestone from Putilowa, Russia. The 
darker grains are glauconite; note the extent to which they are 
altered to opaque limonite, especially in the large grain near the 
edge to the left. 
Another section from Putilowa in which glauconite is somewhat more 
abundant and less altered. 
A thin section of limestone from the zone of Asaphus expansus (top 
of the Walchow) in a quarry opposite Iswos, Russia. 
Note that all three of these slides show the limestone to be made 
up almost entirely of fragments of fossils, largely trilobites, brachio- 
pods, and cystids. All magnified about 10 diameters. 
