GBOLOCJY OF TIJE TOTOMAG BEDS. 49 



clay, whicli serves as a cementing matter, in which tlie grains of sand are 

 embedded. There seems to be some connection between the presence of 

 this day and the incoherence of the material, bnt we find loose sand with 

 little or none of this clay. This is the material which Professor Rogers 

 has called "feldspathic sand." I have seen no feldspar, fresh or decayed, 

 in this material, and the clay, although often quite white and pure, is rarely 

 thti direct product of the decay of feldspar. This argillaceous sand gener- 

 alh' has a white or light gray color. 



In some places the amount of the clay thus intimately mixed with the 

 sand makes up a large proportion of the material, forming from one-fourth 

 to one-third or more of the hulk. Tliis sort of sand is conunon around 

 Fredericksburg, and may also be found in the lower part of the bluff at 

 White House, as well as in many other places. Strange to say, we may 

 find this dispersed clay mixed with coarse sand and even with pebbles. 

 Tiiis is the case at White House, for example, and at Point of Rocks near 

 City Point. The base of the bluff at White House Point to the height of 

 fifteen or twenty feet is composed of a very coarse white indurated sand, 

 containing a large amount of diffused white clay, and in places many 

 quartz pebbles. These are half an inch in diameter and under, and they 

 are irregularly scattered through the mass of the rock. At Point of Rocks, 

 on the Appomattox, seventy feet and more of this material is exposed. It 

 contains pockets and irregular courses of large cobbles, most of them of 

 Potsdam quartzite, seme of them attaining the diameter of ten to twelve 

 inches. Here we find, in one place at least, several masses of the pale red- 

 dish Potomac clay embedded in this coarse mixture. One of these blocks 

 was two and one-iialf feet long and sul)angular-prismatic in shape. There 

 is a large amount of this irregularly mixed coarse material and white day 

 in Trent's Ruach. In one layer here the cobbles of Potsdim aiul other 

 material al)oun(l, and many of them are eight to ten inches in diameter. 



'Chese characters in the sand indicate that it was laid down in agitated 

 and [)robably shallow waters, in which there was little or no sorting of the 

 materials. 



Mica is comparativel}' rare in all parts of the formation, and is hardly 

 ever seen in any of the beds of the Fredericksburg area. It is more com- 



MON XV i 



