JOINTING AS A FUNDAMENTAL FACTOR IN THE 

 DEGRADATION OF THE LITHOSPHERE. 



Plates VI-VIII. 



By FREDERICK EHRENFELD, Ph.D. 



(Read April 14, igi6.) 



This paper is the result in part of a study of the various factors 

 of rock weathering and erosion which I began some years ago and 

 which has been influenced further by a study of the efifects of 

 marine erosion along the north Atlantic coast. 



At a certain point I had the idea of trying to find for mechan- 

 ical weathering a definite factor comparable to the part which chem- 

 ical non-equilibrium plays in chemical weathering ; further study 

 convinced me, however, that there is one factor which is constantly 

 acting in advance of all other factors of both weathering and erosion, 

 and that this factor is jointing. 



In almost all studies and in most textbooks and other geological 

 writings on the subjects of weathering and erosion the matter is 

 usually approached from the point of view of the contact of the at- 

 mosphere, and the results of both weathering and erosion are often 

 spoken of as the attaining more or less perfectly of an equilibrium 

 between the surface of the lithosphere and agents of the atmos- 

 phere. Thus both the formation of " clay " and the formation of 

 a " peneplain " or base level are regarded as the final products of 

 weathering and erosion ; they are the conclusion of a cycle of changes 

 which began in a condition of non-equilibrium, ran through various 

 well-marked stages and ended at last in so-called final products 

 which would or do remain permanent until some general earth 

 change takes place, when a similar cycle will begin anew. If this 

 is a fair statement of the matter, as I think it is, then these are the 

 results of the contact of lithosphere and atmosphere to produce a 

 surface equilibrium. 



363 



