WEATHERING 



29 



monument with paraffine dissolved in turpentine to prevent further 

 decay. Few, if any, tombstones in New England which are over 

 one hundred years old show a polish. A marble slab at North 

 Adams, Massachusetts, for example, upon which an inscription was 

 chiseled in 1865 was practically illegible in 1905 and had to be recut. 

 Such rapid weathering of marble as this is, however, unusual. 

 Tombstones of red sandstone which were erected with the bedding 







-8 











1 



1- 



._.-■-■■ • 



Fig. 5. — Granite broken by two sets of joints. Animas River Canyon, Colorado. 



(U. S. Geol. Surv.) 



planes 1 on edge have suffered severely, because the rain water has 

 soaked down the more porous layers, and upon freezing has forced 

 off sheets of the rock (Fig. 3). Exposed rock surfaces in polar regions 

 are pulverized by frost, producing sand, and fine, dusty material 

 which is shifted by the winds. 



Talus. 2 — The most conspicuous effect of frost is seen in rock 

 masses which are much broken by cracks and joints (p. 258) (Figs. 4, 5). 



1 When rock is arranged in layers it is said to be bedded, and the planes separating the layers 

 are called bedding planes. For a discussion of such rocks (stratified rocks) the student is re- 

 ferred to page 233. 



2 Talus slopes produced in arid regions by changes in daily temperatures are also important. 



