12 Report on the projected Survey of the State of Maryland. 



Another variety of clay, of at least paramount importance to those 

 which have been thus far considered, and which Maryland possesses 

 in great abundance, is that which has been called alum earth. 



The principal deposite of this very valuable material is on the nor- 

 thern shore of the Magothy river, at Cape Sable, in Anne Arundel 

 county. A minute and very able account of this locality has been 

 furnished by one of its original proprietors, Dr. Gerard Troost, at 

 present officially employed as geologist for the state of Tennessee. 

 This account is published in Prof. Silliman's Journal.* The gen- 

 eral features in the geological constitution of this spot, are the fol- 

 lowing, in a descending order : — 



1. Sand, from 20 to 30 feet. 



2. Ferruginous sandstone, - - - - 1 to 2 " 



3. Copperas ore, {iron pyrites,) - - 1 to 2 " 



4. Alum earth — clay embracing iron pyrites and 



lignite, 7 to 10 " 



This stratum is very irregular in its inferior line 

 of separation. It rests upon 



5; A stratum of ferruginous sandstone, - - 1 to 2 " 

 which, if accidentally penetrated, admits the flow of water from be- 

 neath in such abundance, as to put a slop to any further excavation. 



The value of the alum obtained annually from this source is esti- 

 mated at seventy five thousand dollars, and that of the quantity ex- 

 ported out of the limits of the state at sixty five thousand dollars. 



As stated above, this alum earth is associated with a bed of cop- 

 peras ore — the annual product of which has been ascertained to 

 amount to six thousand dollars ; of which one half is exported. 

 This same ore of copperas, as it is termed, which chemists de- 

 scribe as a hisulphuret of iron, occurs in many other situations 

 throughout the district of country which is now being reviewed. It 

 has been found in Cecil county ; it occurs on the shores of the 

 Round bay, in Anne Arundel county ; and at Oxen creek in Prince 

 George's county, it was observed under circumstances leading to the 

 suspicion that there may exist in that place a formation similar to the 

 one at Cape Sable. 



Associated, also, with the clay deposltes, are found abundant for- 

 mations of two varieties of iron ore, which, as they are but seldom 

 used for the extraction of the metal, may be properly mentioned here. 



* Vol. iii. p 8. 



