400 TRANSACTIONS OF THE 



yielded no mineralized fossils. Beside the modern leaves, 

 etc., of trees, impressions of two forms of Unios, entirely 

 without the shell, have been dug from the black clay. 

 From the form and impression left by the shell, I am led 

 to believe that they belong to the common living species 

 which have frequently been taken from the pools of dirty 

 water in the adjoining black bogs, and which may still be 

 found in the mud of the brick ponds in this vicinity, as 

 well as in Winan's Cove. These two species are Anodon 

 flluviatilis Lea, and Unio complanatus Say. The above 

 record is most suggestive, because of the very modern 

 period of construction of this comparatively thick series 

 of sedimentary beds. Of course, it is a fact of actual 

 knowledge that the volume of water carried by the 

 streams entering our Maryland Coastal Plain was much 

 greater and consequently far stronger a few years ago 

 than it is at the present time. It is not therefore necessary 

 to assume a general depression of the tidewater region to 

 account for the presence of this formation. 



The accumulations of sediment over the low levels near 

 the mouths of small creeks, such as Gwynn's Falls, Her- 

 ring Run, Stemmer's Run, etc., have filled them up more 

 than five feet within the last thirty years. If we take this 

 fact in connection with the broader relations of degrada- 

 tion and deposition in this region, we shall see that the 

 accumulation has exceeded the seaward transportation by 

 a large surplus. Evidences of a general depression of the 

 Coastal Plain immediately preceding the formation of these 

 marshes seem to be w^anting. The erosion and degrada- 

 tion which laid bare the areas to be occupied by the 

 marshes was not of uniform intensity, and accordingly 

 their base lines are not all on the same level. So we 

 see evidences of local forces cutting deeper in some places 

 than in others, and we fail to find a general distributign 

 of this particular kind of sediment over the low levels of 

 this region. 



