File:Proctor Brothers' Quarry Fig 1 Plate XXXI WBClark 1898.jpg

English: Plate XXXI, Figure 1 of 1898 publication called Maryland Geological Survey Volume Two. Caption:
Proctor Brothers' Quarry, Cambria, Harford County
The text of the book refers to the figure as follows:
All of the quarries along the line show a great many series of joints which both aid and hinder the working of the quarries. The principal or bedding joints as observed in the Proctor Brothers opening (shown in Plate XXXI Fig 1) strike cross the cleavage and dip at an angle of 42 degrees to the southwest. ... In addition to this most clearly marked jointing, there is a second series of joints dipping at an angle of 26 degrees with the same strike and another set of joints which dip at about 80 degrees to the northeast with their strike normal to the cleavage. These three systems free the rock in large rhomboidal slabs and they if they existed alone would be very valuable aids in quarrying the rock. Unfortunately besides these somewhat uniformly inclined joints, there are a great many other jointing planes developed through the beds which do not seem to be conformable to any system of arrangement. They cut each other at all angles and intersect the plane of cleavage either acutely or with considerable obtuseness.