Specimens Recently Collected in Serpentine Area ^^ 



and aragonite. Associated with the serpentine and apparently 

 indicating the location of a fault line or shear zone, was a vertical 

 series of very hard amphibolite or antholite schists, identical with 

 the rock struck at a depth of 200 feet in a well boring at 

 Bischoff's brewery, Stapleton, also on the eastern edge of the 

 escarpment. What is apparently a continuation of this series 

 may also be seen outcropping on the surface along the eastern 

 side of Pavilion Hill, where in one place it is an almost black 

 hornblende rock. Another shear plane was occupied by a band 

 of chlorite schist and talc, which attracted considerable atten- 

 tion on account of its conspicuous coloring and also because it 

 caused the contractor more or less trouble by slipping. 



The great variation in the color and texture of the rock from 

 place to place throughout the area might seem to preclude the 

 probability that it was all derived from one source ; but the field 

 observations, taken in conjunction with the determination of the 

 mineral constituents by microscopic examination, indicate conclu- 

 sively that it all had a common origin and that this was a basic 

 igneous rock. 



The fact that the most extensive fracturing and shearing of 

 the rock, accompanied by the greatest variety in the rock and its 

 associated minerals, occurs along the face of the steep eastern 

 escarpment is significant. It evidently represents a zone of dis- 

 turbance and at once suggests a fault as the cause of the escarp- 

 ment, and the accompanying shearing and slipping as the con- 

 trolling factor in the evolution of most of the minerals that are 

 found along the shear planes. All the phases of the antholite 

 schist may be seen, sometimes in a single hand specimen, from 

 the hard massive or crystalline form to that which is flattened 

 or foliated or lengthened out into fibrous asbestos. Heretofore 

 we have always called this latter mineral "fibrous serpentine." 

 a name that must now be abandoned. 



