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A Comparison of the Plant Succession on Hudson River 



Limestone with that on Niagara Limestone, 



Near Richmond, Indiana. 



M. S. Markle, Earlham College. 



The outcrops of bed-rock in the vicinity of Richmond, Ind., consist 

 of two kinds of rock, namely, Niagara limestone and Hudson River lime- 

 stone. The marked differences between these two kinds of rock make 

 a study of the plant succession on the outcrops very interesting. 



The principal outcrop of the Hudson River limestone is in the gorge 

 of the Whitewater River, where it passes through the city of Richmond. 

 This gorge is about three miles long, 200-300 feet wide and up to 100 feet 

 or more in depth. This gorge is supposed to have been formed immedi 

 ately after the ice age. 



Outcrops of Niagara limestone occur only south of the city, the 

 principal ones being in the gorges below the falls at Elliott's Mills and 

 at Elkhorn Mills, two and three miles southeast of Richmond, respec- 

 tively. The present report is the result of a study of the outcrops in 

 the Whitewater gorge and the gorge at Elkhorn Mills. 



The principal differences between the two kinds of rocks is in their 

 physical character. The Hudson River limestone is composed of alter- 

 nate layers of calcareous shale and rather soft limestone. These con- 

 stituents vary greatly in amount, the rock consisting in some places al- 

 most entirely of shale and in others almost entirely of limestone. Gen- 

 erally, however, they are about equal in amount. The Niagara limestone 

 is not accompanied by shale, but consists entirely of hard thick-bedded 

 limestone. 



On account of the physical character of the Hudson River limestone, 

 the plant succession in the Whitewater Gorge is very rapid for a rock 

 cliff. The stage of the succession of any part of the cliff is due to the 

 length of time that has elapsed since the cessation of active undercut- 

 ting by the river. All stages of succession from the plantless rock to 

 the climax mesophytic forest are to be found. The earliest stage in the 

 succession occurs where the cliff is being actively eroded by the river. 



