372 EHRENFELD— JOINTING AS A FUNDAMENTAL FACTOR 



the destructive influence of those joints which are part of the funda- 

 mental nature of the hthosphere itself. 



The old problem of marine planation which was so much dis- 

 cussed by the geologists of the former generation had at least ele- 

 ments of truth in it, elements which are, I believe, covered by the 

 mutual action of joints and marine attack producing degradation of 

 the Hthosphere below sea level. So that marine planation does act 

 to produce a further degradation of the hthosphere below the base 

 level of erosion or below Davis's peneplain. That to restate the 

 point, weathering and surface erosion proceed by the usual well ob- 

 served methods and reduce the hthosphere to residual sands, clays 

 and peneplain but this does not complete the possible further degra- 

 dation of the surface of the Hthosphere because the joints which 

 have developed as one of the primary features of the Hthosphere 

 extend on down below sea level and granted an agent of transpor- 

 tation, for instance the sea, and its currents and tides, there is still 

 the sub-base level process of degradation proceeding. It must be 

 remembered that the sea is one of the most powerful reducing and 

 transporting agents known and acts always against the continental 

 masses somewhere, so that a system of jointing once started and the 

 sea playing against it, the action of reduction is carried along rather 

 quickly as geological time goes. I have personally observed in the 

 garnet-mica-quartz schist rocks south and west of Portland Harbor, 

 Me., the complete reduction from jointed blocks in the sea cliffs 

 down through various stages of pebbles and gravels to sands which 

 are composed of quartz sands and the garnet crystals from the mica 

 schists, while the mica is by tidal action carried out beyond the shore 

 to deeper water (Fig. 3. Plate VH). 



I put some considerable emphasis upon this because the actual 

 beach evidence and the evidence from sands and gravels on the fore- 

 shore in many cases fail to show all the intermediate stages so that 

 there is here suggested the possibility of many coarse and fine sands 

 in the older geological formations having been formed by a process 

 of rapid joint splitting, beach grinding and tidal distribution of the 

 residue. The rapid accumulation and great diversity of sands, 

 gravels and conglomerates of the Pottsville, for instance, may have 

 been due to such combined action of a jointing structure and a rapid 



