282 PROCEEDINGS OP THE ACADEMY OF [1880. 



October 27, 1879. 



THE IRON ORES AND LIGNITE OF THE MONTGOMERY CO. VALLEY, 



BY HENRY CARVILL LEWIS. 



The discovery ol lignite in the iron ore region north of Phila- 

 delphia introduces some new considerations in the study of its 

 geology, and has a direct bearing upon the age of its iron ores. 

 Lignite was found in this valley many years ago, but was supposed 

 to be Triassic, and therefore unimportant.' Before judging of the 

 connection that the occurrence of lignite in the Montgomery Co. 

 limestone valley will have with the geology of the Atlantic coast, 

 it will be important to enumerate other localities of a similar 

 nature where that mineral has been found. 



In his Geology of Vermont, Prof. E. Hitchcock described an 

 occurrence of lignite in a similar position at Brandon, Yt., and 

 proposed a theory which excited much attention, but which has 

 been rejected by many geologists. It was shown that a steeply- 

 dipping stratum • of lignite lay within beds of plastic clay, kaolin 

 and iron ore, all dipping steepl}^ southeast. The iron ore deposit 

 was sometimes 100 feet deep, and all these beds rested against a 

 limestone which had the same steep dip. Mottled clays were 

 described as similar to those of Martha's Vineyard and the Isle of 

 Wight, and much of the formation was said to resemble a meta- 

 morphosed mica schist. The stratum of lignite was opened from 

 near the surface to a depth of 80 feet, and was used as coal. It 

 proved to be generally dicotyledonous, and to contain twigs and 

 fruits which belonged to a tropical climate, and which Professor 

 Xesquereux referred to a Tertiary epoch, probably Miocene. From 

 this discovery, Prof. Hitchcock proposed the theorj^ that all the 

 limonite iron ores of the Atlantic coast in similar geological posi- 

 tions were Tertiary and of oceanic origin. On the other hand, 

 it was argued that an isolated example was not sufficient to estab- 

 lish such a wide conclusion, and the lignite was regarded as locally 

 :formed by having been washed mto an existing cavern in the 

 limestone floor. 



The next occurrence of lignite is a very similar one at Pond 

 Bank, near Chambersburg, Pa., described in an interesting 



» F. Piof. Leidj, Proc. Acad. Nat Sci., Phila., 1861^ 77. 



