480 IOWA ACADEMY OF SCIENCE Voi.. XXVI, 1919 



parts ; the smaller part, which is approximately 10x7x5 feet in maxi- 

 mum dimensions, has sustained all the movement since it rests on 

 top of the ground while the larger part penetrates the soil to an un- 

 known depth. The faces formerly in apposition and now separated 

 by the trunk are readily distinguished. The original cleft in which 

 the sapling sprouted was at an angle of about 45 degrees. The 

 effect of starting its growth in this unnatural position is still ap- 

 parent in the trunk whose lower part is permanently bent. As the 

 tree grew the smaller part of the stone was not only shoved over 

 but was also rotated through an angle of over 45 degrees since the 

 face against which the trunk shoves is now vertical or slightly be- 

 yond that position. The volume of the smaller part, according to 

 the dimensions cited above, is 350 cubic feet. Dividing this by two 

 to allow for the irregularities of the stone, its weight, at 175 pounds 

 per cubic foot, would be over fifteen tons. This figure gives some 

 conception of the shoving power which this particular tree has ex- 

 erted during its growth. Many of the larger roots of the tree have 

 grown out of one end of the cleft and thence into the earth to avoid 

 the main mass of the stone which extends not only directly under 

 the tree but also into the earth beneath the smaller part of the stone. 



The tree is a thrifty elm, Ulmits americana, about fifty feet high. 

 The trunk within the cleft and for some distance above the stone is 

 rounded-flattened or oval in cross-section and its dimensions at the 

 top of the boulder are four and one-half by two and one-half feet. 



This example of a split boulder, possibly the only one illustrating 

 this feature in Iowa, compares favorably with those illustrated in 

 current textbooks. It is hoped that the good citizens of Nashua and 

 vicinity may long preserve it from injury. Students of natural 

 phenomena for decades to come will marvel at the power of the 

 seedling elm which has rent the massive boulder in twain. 



The Department of Geology, 

 The State University. 



