DIVISION EIGHT — SCIENCE. 555 



port more specifically upon it. There are three distinct varieties of geologi- 

 cal waymarks among these exposed and weather-worn rocks on the north- 

 east postern of the narrow gorge known as "Devil's Gate," to-wit : slick- 

 ensides, glacial enamelings,* and water carving. 



Slickensides. — "Polished and scratched or striated rock-surfaces, ex- 

 hibited on the opposed faces of veins or faults, or occasionally between lay- 

 ers of stratified rocks where they have moved one upon another," — Stan- 

 dard Dictionary, iSg^. 



These marks were probably made when these rocks were first upheaved 

 from their original bed at the bottom of the ocean, and pressed against each 

 other so hard as to produce a glaze-film by the heat of friction ; but they 

 could possibly have been made by earthquake movement at a later period ; 

 and these particular ones could also have been made by glacier movement, 

 because they lie in a horizontal position and not vertical or at some angle ot 

 elevation, as slickensides usuallv do. This fact of their horizontal position, 

 and of close association here with other marks certainly of glacial origin, 

 and of their alignment with the most probable course of the glacial move- 

 ment at this point, led me at first to class them as ' ' glacial scratches ' ' or 

 striations, as spoken of in the above document. But Mr. Ossian Guthrie, an 

 expert glacialist of Chicago, examined them with me early in February, 

 1895, a^^d pronounced them unquestionably "slickensides," notwithstand- 

 ing their unorthodox position ; and I concurred in that as perhaps the greater 

 probability, t 



Glacial Enameling s. — These are the marks " like patches of polished 

 chisel work ' ' spoken of in the June 2d document. They are not ' ' scratches ' ' 

 in the ordinary sense, nor striations, but rather gougings, with a thin shell 

 of glassy-like glazing on the surface, which were produced by a friction so 

 great as to generate heat enough to melt or vitrify the surface of the rock 

 at points of heaviest contact. The glaze-film or enamel would of course be 

 harder than the body of the rock, and thus preserve their character — other- 

 wise they would have been worn away by water or weather long ago ; and 

 in fact there are many spots discernible where flakes of the enamel have 

 cracked and peeled off. These marks are on the surface of what is appar- 

 ently an obtruding head of tilted and fractured bedrock that stands partly 

 in contact with the slickensides rocks. It lies in the line of right-oblique 

 movement which would naturally have been produced by a glacier moving 



*"I noticed in many places, as we approached Lake Tenaj'a. the polishings and scorings of ancient 

 glaciers. * * It is wonderful that in granite so decomposable these old glacial surfaces should remain 

 as fresh as theday thej- were left bv the glacier. But if ever the pjlished surface scales ofif, then the dis- 

 integration proceeds as usual. The destruction of these surfaces by scaling is in fact continually going 

 on. '—Prnf. Joseph LeConte, in Overland Monthly, Nov., iS8;; page $01. 



What Prof. LeConte calls "polishings," I have called •' enamelings," because this latter term better 

 expresses their distinctive character && glazed surfaces— entirely different from any water-worn or sand- 

 scoured smoothness. 



tThree or four months later, Capt. D. M. Greene, late of U. S. Army, discovered there one series of 

 slickenside striations which had another series crossing them diagonally. -"^nd this second grooving 

 may have been produced either by glacier or by earthquake movement. 



