326 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



DESCRIPTION OF PLATES 



(Illustrations slightly reduced in size) 



Plate 1 



FiGUBES 1-5. A series of clay lime concretions from the glacial clays of Scho- 

 harie Creek, N. Y., and Barry's Bay, Ontario, showing the evolution from 

 the simple type to the loesspiippchen (fig. 4) and the animal forms (fig. 5). 



FiGUEES 6-8. Petrified "peanuts" showing formation from fresh-water shells 

 coated layer after layer with lime (6) until their original outlines are 

 lost (S). 



FiGUBES 9, 10. Mud concretion of present day origin from the Illinois bank 

 of the Mississippi River. The fractured interior suggests the origin of 

 septaria. 



Figures 11-13. Clay lime concretions from glacial clays of Vermont exhibiting 

 three phases in the formation of the emblematic forms. 



FIGURE 14. A specimen from Texas, supposed to represent a fossil turtle. 



Plate 2 



Figure 1. A clay lime septarium, i/^ natural size, from the Devonian rocks of 

 western New York, with the shrinkage cracks filled with crystalline cal- 

 cium carbonate. The original polygons of large size are in process of 

 subdivision into smaller areas by secondary shrinkage. 



Figure 2. A siliceous pseudomorph resulting from the solution of a septarium ; 

 about Vj natural size. Calcareous septa in the original septarium were 

 replaced by silica which because of its little solubility in water was left 

 behind when the substance of the nodule itself was dissolved away. From 

 fuller's earth deposit at Groveton, Ga. 



Figure 3. A primitive ganoid fish forming the nucleus of a clay ironstone con- 

 cretion from Mazon Creek, 111. Slightly enlarged. 



Figure 4. An ironstone nodule from Mazon Creek which when split in half 

 exhibited a fossil horseshoe crab. 



Plate 3 



Figures 1, 2. A concretion of iron hydroxide, slightly less than natural size, 

 and a portion enlarged, showing the regular arrangement of the markings 

 of the first, second, and third order. Cannon Ball River of North Dakota. 



Figure 3. Ironstone concretion from Mazon Creek, 111., split along the line of 

 the seed fern frond which served as a nucleus. 



