THE GEOLOGIST AT BLUE MOUNTAIN, MARYLAND 



BY 

 CHARLES D. WALCOTT 



Most of the summer visitors at Blue mountain, Maryland, 

 give little thought to the origin of the mountain, nor how it 

 came to be a ridge rising so boldly on the west from the Cum- 

 berland valley and on the east overlooking the mountain valley 

 to the foot of the Catoctin ridge, which rises above the plain 

 stretching thence southeastward to Washington. 



During the summer of 1892 the writer discovered that the 

 rocks forming the crest of the Blue ridge belong among the 

 oldest formations deposited in the Appalachian trough, since they 

 carry types of life occurring in the most ancient fossiliferous 

 rocks on the North American continent that are distinguished 

 by a recognizable fauna ; the geologic structure also shows that 

 these rocks rest upon the ancient sea-bed of the Appalachian 

 trough, and that they are of the same relative geologic age as 

 the Cambrian rocks that occupy an equivalent stratigraphic 

 position in Vermont, New Jersey, New York, Virginia and Ten- 

 nessee. 



The recent work of Dr G. H. Williams demonstrates that, with 

 one partial exception, the older crystalline rocks underlying the 

 Cambrian strata have hitherto been misinterpreted and misun- 

 derstood by the geologists who have studied them. Instead of 

 being sedimentary formations originally deposited in the sea-bed, 

 they are volca,nic rocks and almost identical with the lavas 

 found in Nevada, Wyoming and in many portions of the Rock}' 

 mountain region. This discovery proves that the laboratory of 

 nature produced a certain type of volcanic rock almost at the 

 beginning of the evolution of the North American continent, and 

 again produced the same tjq^e many millions of year.'^ afterward 

 on the western side of the continent. 



The broad mountain crossing the Pennsjdvania-Maryland line 

 includes eastern and western border ridges and an intervening 



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