28 Life of a Fossil Hunter 



assistance given me when I most needed help, it is 

 doubtful whether Iowa would have secured this 

 treasure. My months of patient labor on the leaves 

 had convinced the authorities that my work on the 

 mosasaur would be faithfully done. 



Before closing this account of my work in the 

 Dakota Group, I should like to say a few words 

 about the manner in which the nodules are formed 

 around leaf impressions, a subject of which I have 

 made a careful study during years of exploration. 

 The illustrations (Fig. 5, a and b) show the 

 nodules before they are opened, and the open 

 specimens before they have been trimmed, as in the 

 other cuts. 



The mother rock, or matrix, as it is called, from 

 which these concretions come, is quite soft and 

 easily disintegrates into yellowish sand under the 

 influences of the weather. Through this yellowish 

 sandstone are scattered countless leaf impressions 

 and their counterparts, but on account of the soft- 

 ness of the matrix it is impossible to work out any 

 leaves from the inside of the rock masses, and we 

 should lose them altogether were it not for the fol- 

 lowing natural process : 



Falling from the trees that grew along the shore 

 of the Cretaceous Ocean, these leaves were covered 

 with sand by the incoming tide. Some, falling stem 

 first, were turned over into a U-shape; others are 



