376 EHRENFELD— JOINTING AS A FUNDAMENTAL FACTOR 



which would be much slower in their accumulation and would 

 hardly be in block or even pebble form at all. Secondly the eleva- 

 tion of the original beds could scarcely have come about without 

 fracturing as there is no reason to suppose that the beds were so 

 deep seated as to come within the " zone of flowage," the elevation 

 was not probably great and would under the circumstances be in- 

 cluded in the zone of fracture. 



From the paleogeographic point of view the subject is possessed 

 of possibly more than passing interest because of the fact that it 

 introduces into the study of unconformity or non-conformity a 

 means of determining the time factor, and also the means of deter- 

 mining the fact of a break in the succession of deposition, and it 

 may also serve to determine the fact of a stratigraphic break with- 

 out the recession of the sea. Walcott's idea of the events of the 

 formation is practically sub-marine planation, a thing which could 

 hardly occur without a very rapid cause of breakdown in the lime- 

 stone, such as would result from jointing. 



I have no desire to burden the nomenclature of the science with 

 any new terms, but the idea of jointing causing a record of a dis- 

 conformity which would otherwise be lost seems to me worth the 

 notice. If the displacement of the lower limestones had occurred 

 without jointing it is most probable that there would not have been 

 enough disintegration to have left any record unless the time inter- 

 val had been long enough to bring about the usual atmospheric 

 weathering. In the physical conditions supposed by Walcott the 

 development of jointing would also act to prevent the persistence 

 for any great length of time of a barrier to faunal migrations. 



In connection with the discussions of the conglomerates of the 

 Pottsville above, reference is made to the arkose conglomerates and 

 sands of the Newark. Since the granite pebble conglomerates of 

 an arkose character are now to be observed in formation along the 

 coast lines where rock disintegration and degradation are controlled 

 by joints and may easily be seen to be so, as along the coast of 

 Maine for instance, I believe it to be probable that the arkoses of 

 the Newark of the Atlantic coast states are also due to rock de- 

 struction caused by joints, inasmuch as the sediments are composed 

 of materials which show a mechanical disintegration always in ad- 



