GEOLOGY OF TIJE POTOMAC BKDS. 57 



and other colors, due to iron oxide. Irregular masses of it are sometimes 

 sandy. It has often small bits of plants and fragments of lignite, l)ut no 

 Hgnitic entire trunks were seen. The bottom of this clay is easily disrin- 

 guished from the top of No. 3 by its peculiar structure. At the same 

 time the clay of No. 3 is rather more sandy. 



No. 3 consists of alternations of gray clay and argillaceous sand, 

 showing a distinctl\- bedded arrangement, but much invgularity in the 

 thickness and other features of the constituent beds. The lower portion 

 has a predominance of sandy matter, but the clay increases as we ascend, 

 and in the top it exceeds the sand in amount. The sandy layers of No. 3 

 are gray in color and more argillaceous than No. 1. They have many 

 blotches and streaks of vellowish-brown and reddish colors mingled with 

 the dingy gray, which is the princi[)al color, and the layers swell up and 

 thin away in the most irregular manner. At the base of No. 3 and resting 

 on No. 2 we find in several places two or three feet of a tender ash-gray 

 shale, with patches and irregular lenticular thin partings of fine sandy 

 matter. This is the portion that contains the recognizable plant-impres- 

 sions. This portion, and indeed all the clay of No. 3, is easil}' distin- 

 guished from the Variegated Clay b}- most of the workers in the Baltimore 

 clays, and the plant-bearing part is called "shelly or slaty clay." 



No. 2 seems to be simply the upper part of No. 1, which has been 

 impregnated with iron. It is not universally present, being generally 

 wanting when formations younger than the Variegated Clay rest on No. 1. 



No. 1, at Federal Hill, has clay balls with some pebbles, and it is 

 stained reddish in some irregularly shaped portions by iron oxide. It is 

 here very friable, appearing as an incoherent sand. It has very little 

 diffused white clay or so-called kaolin. It is sought for on account of 

 the comparatively pure sand that it }ields. 



The Variegated Clay seems to bo a northern fi>rmation. As stated 

 before, the point farthest south at wliich it has been seen with its charac- 

 teristic features is Fort Washington. Here it is much thinner than between 

 Washington and Baltimore. If it api)ears in Virginia, it occurs without 

 the features which are so conspicuous farther north. It has not been 

 recosrnized in that State. 



