52 PHYSICAL GEOGRAPHY 



of that portion of the territory of Maryland, occupied by Cal- 

 vert county. The cliffs of the latter county, previously 

 described at page 32, present an almost continuous accumula- 

 tion of marine shells and exuviae, reaching to an elevation of 

 nearly one hundred feet above tide, and disposed apparently in 

 three distinct layers, though not always recurring together, 

 composed of the same kinds of fossils. It is impossible to 

 assign its extent below tide, which is doubtless very great, as 

 in one instance it has been dug into the depth of seventy feet 

 below high-water mark without penetrating through the fos- 

 sils. Whether the whole of this immense deposile has been 

 made during one or more geological periods it is difficult to 

 say; and to which of the tertiary epochs it mainly belongs 

 has not yet been satisfactorily determined. The number of 

 marine shells contained in it that have been so far collected 

 amounts to about one hundred and forty species ; but the 

 proportion of recent and extinct species among them, has not 

 yet been ascertained. The most constant attendants upon 

 these marine shells are the ribs and vertebras of a species of 

 Delphvivs^ the palatal bones of some fish, and a great number 

 of shark's teeth of all sizes. 



In one locality, near the extreme end of the peninsula, all 

 the fossils have their analogues living either in the waters of 

 the Chesapeake bay or adjacent ocean ; whilst in two other 

 localities, one at the edge of the tide, on the Potomac, the 

 other eight feet above it, on the Patuxent, the deposites consist 

 exclusively of the Ostrea Virginica. 



The upper portions of the great arenaceous and argillaceous 

 formations that have just been described in reference to their 

 fossil contents afford a vast supply of excellent iron-ores, prin- 

 cipally composed of carbonate and hydrates of iron. This is 

 also the locality of extensive deposites of fire proof clays, and 

 other aluminous earths used for the manufacture of bricks, of 

 which the beautiful pressed-bricks made in the vicinity of Bal- 

 timore are not surpassed by any in the world ; whilst the banks 

 of the creeks and rivers furnish the more ordinary clays that 

 are employed for making the various kinds of pottery. The 

 deposite of lignites and pyrites, already referred to as occurring 

 at Cape Sable, on the Magothy, furnishes the material from 



