GEOLOGY AND PALEONTOLOGY OF THE SCHOHARIE VALLEY 121 



Lorraine shales, the succession being an abrupt one. The source 

 of the pebbles of this conglomerate could only have been in the 

 crystalline highlands, i. e. the Adirondacks, and the Appalachian 

 protaxis of New York, Pennsylvania and the Southern States, 

 for we know, of no other source for the quartz pebbles than these 

 crystallines. That all the material except the indestructible 

 quartz has been removed, indicates that these beds mast have 

 been repeatedly worked over by the waves. The sudden suc- 

 cession of these conglomerates on the soft shales in central New 

 York is explained by the condition outlined in chapter 1. A 

 stationary or a gently rising sea floor will cause the shore to 

 migrate seaward and carry with it the shore deposits which will 

 gradually creep out over the sand deposits of what was formerly 

 deeper water. If the recession of the shore is a slow one the 

 thickness of the shore deposit, i. e. the conglomerate, is mostly 

 uniform. On the other hand a rapid recession of the shore will 

 result in a progressively thinner and thinner accumulation of 

 the shore deposits over the deeper water beds.^ 



If we picture to ourselves the condition of depoisition during 

 Lorraine time, we must realize that the edge of the Lorraine 

 sea touched the crystalline shore, from which the sands and 

 clays were derived. That being the case the Lorraine deposits 

 naturally overlapped the preceding Champlainic deposits, a 

 result we would expect where a progressive subsidence of the 

 sea bottom takes place. Along the shore the deposits must 

 have been conglomerates and coarse sandstones and at intervals 

 some of these must have spread out over the finer deposits, thus 

 giving us the abrupt alternations commonly seen [fig. 28A]. At 

 the end of Lorraine time, a gradual rise of the shore and a conse- 

 quent retreat of the sea margin appears to have taken place, ac- 

 companied in the Appalachian region by considerable folding and 



^Rivers from the rising Green mountain chain no doubt formed a power- 

 ful agent aiding the waves in carrying the pebbles westward and in 

 thoroughly rounding them. The red sands and muds of the Medina, de- 

 rived from the oxidized crystallines were probably also in part subaerial 

 in origin. 



