Lesley.] ■^'± [Jan. 2 and Feb. 6, 



A great fault runs along the foot of Bald Eagle Mountain, and on the 

 west side of this fault the same formations are seen descending vertically. 

 They then curve sharply, and pass horizontally N. Northwestward under 

 the Alleghany Mountains, as shown in diagram section fig. 4. 



This diagram section is constructed from the dips of the Upper 

 Silurian, Devonian and Coal Measure rocks, observed on a survey of the 

 road from Bald Eagle Furnace up Emigh's run and Laurel Creek to the 

 crest of the Alleghany Mountain. The measurement of the curves of 

 the different layers of this upturned mass, taken at every thousand feet, 

 as shown in the diagram, result in giving a slope of 50° to 54° to the 

 bassett edges of the broken mass. 



It is evident that the upslide of the other section of the broken mass 

 has conformed to this slope, and that the uniform dip of 54^ =b observ- 

 able for miles along the S. S. East foot of Bald Eagle Mountain (as repre- 

 sented in Juniata Section, and Sections AB and CD) is perfectly ex- 

 plained by the diagram. 



This is the first time, I believe, a solution of this difficult problem in 

 structural geology has been reached ; and its bearings upon similar phe- 

 nomena attending upthrow-faults and broken anticlinals in other regions 

 will be noticed by geologists. 



The theoretical deductions from this solution are important. 



It proves that the original fault was in a vertical plane, and not on a 

 slant. 



It proves that the lower Silurian Limestone mass has ridden upon this 

 slope to a considerable height, probably several miles, in the air above 

 the present surface. 



It illustrates the grea,t erosion of the country, amounting to thousands 

 of cubic miles of earth crust, inckidiug the coal measures (which are 

 preserved on Broad Top, 20 miles to the southeast,) and gives us the 

 source of the Cretaceous and Tertiary deposits of New Jersey and 

 Delaware. 



It leads me even to suspect the existence of a subterranean range of 

 Laurentian Mountains (with their usual magnetic iron ores) at the bottom 

 of the fault ; this range determining the line of fractvire. 



It accounts for the general S. S. E. dip across the whole valley, Tussey 

 Mountain, and as far as Huntingdon. 



It assures us that the brown hematite ore beds of the district studied 

 in this report belong to rocks of different ages, and are ranged in parallel 

 belts according as the formations which carry them descend successively 

 (S. S. Eastward,) beneath the present surface. 



It confirms the opinion that the quantity of ore in these belts is not a 

 local accident at each of the ore banks, but bears a fixed relation and 

 proportion to the oiitcrop run of the ore-bearing limestones, lengthwise 

 of the valley ; and, therefore, that any estimate of the quantity of ore we 

 may make by examining the diggings, must fall short of the actual 

 quantity of ore to be mined in future years in this valley. 



