very much broken up and covered with massive granitic eruptives. This is on the line north of Silver Canyon. South of Silver Canyon about five miles, the section as viewed from the high ridge south of Tollgate Canyon is diagrammatically represented in fig. A. The quartzite of the western limb of the syncline is hidden by an intervening ridge, but the syncline of the upper limestone and the two minor synclines to the eastward are clearly defined. The most easterly, on the eastern slope of the range, was not seen at near view, but it appeared to be as represented in fig. A. The east fork of Black Canyon cuts entirely through the quartzite (No. 3) and into the lower limestone. The syncline has flattened out, and its western limb is nowhere overturned to the eastward. The quartzite (No. 3) is much contorted and broken by minor faults. This is most noticeable about midway of the section and also within a few hundred feet of the upper limestone, where there is a series of sharp anticlinal and clinal folds, as shown in fig. D, as well as in the enlarged view, fig. E. The depth of these minor synclines is about 300 feet. They appear to have been formed largely by the slipping and compression of a series of argillaceous and thin-bedded quartzites that are between the upper limestone and other portions of the quartzite series. The upper limestones form a broad, somewhat shallow, irregular syncline, upon which, at the summit, rest about 200 feet of arenaceous shales and thin, interbedded quartzites. This shallow syncline extends southward to Tollgate Canyon, where it is much broken, as shown in the sketch made by Mr. Gilbert.* South of Tollgate Canyon there. appears to be a broad, broken syncline, with the upper limestone (No. 2) at the summit.

syn

Viewing the White Mountain range from the western slope of the Sierra Nevada, north of Big Pine, it is evident that several transverse or oblique faults break the syncline that rests on the western slope of the range. The strata are displaced on the south side of Black Canyon, and also about five miles to the north. About twenty miles north of Silver Canyon the sedimentary strata are more broken and are apparently covered by eruptive rocks that form the higher portions of the range near White Mountain peak.

The only point that I visited on the eastern side of the range was the section exposed on the northern and western side of Deep Spring valley. On the northern side eruptive granites conceal the greater portion of the sedimentary rocks, but on the western side, nearly southwest of Antelope Spring, are some very fine illustrations of open anticlinal and synclinal folding. This is shown by fig. F.

* Loc. cit.

FIG. A.-Diagrammatic section of the White Mountain range as viewed from the high ridge south of Tollgate Canyon. 2, upper limestone; 3, quartz

ite and shale series.

FIG. B.-Theoretical section of range south of Silver Canyon, to illustrate character of syncline. 2, upper limestone; 3, quartzite and shale series; 4, lower limestone.

FIG. C.-Syncline on the north side of Silver Canyon. 1, upper shale; 2, upper limestone; 3, quartzite and shale series.

FIG. D.-Section on the east fork of Black Canyon. 1, upper shale; 2, limestone; 3, quartzite series; 4. upper portion of the lower limestone. FIG. E.-Anticlinal and synclinal folds occurring at x in fig. D.

FIG. F.-Outline of folding of limestone imbedded in quartzite and shales, western side of Deep Spring valley. a-b, fault.

EAST

As seen from the western slopes of the White Mountain. range, the next range to the eastward, Silver Peak, is apparently a monocline facing westward; but from the known structure of the Great Basin ranges, such as those of the Eureka district, Nevada, the Oquirr range, Utah, and others illustrated by the geologists of the Wheeler Survey, it appears that in the broad Paleozoic area between the Sierra Nevada on the west and the early Paleozoic shoreline on the east (Colorado) a period of folding and thrust faulting was followed by a period of vertical faulting, which displaced the strata that had been folded and faulted in the preceding epoch. The extent and character of this disturbance can be determined only by a careful study of each of the mountain ranges for a distance of over five hundred miles east and west and probably a thousand miles north and south; and the great geologic problems will not be fully solved until the areal geology of the region between the 109th and 119th meridians shall have been mapped.

ART. XVII.-Notes on the Southern Ice Limit in Eastern Pennsylvania; by EDWARD H. WILLIAMS.

THE accompanying map shows what has been done during the past year, and the boundary has been extended from the Schuylkill to Lock Haven. There probably does not occur as diversified a field, and one more fortunately situated, than that. which stretches from the Delaware river to the Alleghany Mountain in Pennsylvania. The measures from the Archæan to the Trias lie under all states of deformation and weathering and, forming all arrangements of mountain and valley, opposed all angles of trend and slope to the approach of the glacier. The lithological and fossiliferous characters of those measures are frequently so well marked that their fragments can be quite readily recognized under all conditions of weathering. The streams of the region run toward all points of the compass, and the Delaware, Lehigh, Schuylkill, and Susquehanna are of constantly large volume, and flow through gaps of great age as shown by their low angles, and over preglacial bottoms. The peculiar systems of parallel ridges and valleys of the region bring great differences in barometric level within small areas; so that the resistance to advance of the ice varied greatly within short distances and, at times, created a shear in the interior of the glacier. The varied river systems also distributed the glacial trash where it could be again taken up by

the advancing ice. The glacial discharges and final ablation were made under all conditions of freedom or damming, as the ice-front faced an ascending or descending valley, or rested against a ridge which it could not surmount.

In view of the fact that many writers seem to have forgotten how ice acts in its first advance over a previously unglaciated region, it seems necessary to discuss the subject. Ice erodes and accumulates and, as the country was generally covered, the erosion was of the surface covered, and the accumulations were also from that surface, which, before the advent of the ice, was more or less deeply covered with soil of decomposition. What became of this old soil and its more or less decomposed fragments? In the west, where drainage favored, they were washed away by the glacial floods in the shape of mud and sand, and so distributed that their identity is lost. It is only where drainage has been opposed by the ridges and upward sloping valleys of the Appalachian system, and all waters forced to escape sub-glacially, that we can fully study the deposits of the first glaciation.

The first advance of the ice carried a burden of rotten material. The soft underlying parts were immediately powdered, and whatever resisted immediate destruction was more or less rotted and generally oxidized; but, as it was opposed to a soft surface, its fragments were only rounded into a highly oxidized gravel that was mixed with the clays and sands of the old soil. It was only after a continuance of erosion that the solid rocks were reached and attached to the base of the ice. As this took place at a distance from the ice front, the fresher fragments were carried against the softer surfaces where the ice had as much of a cutting effect as its burden, and no scoring or grooving occurred-only a planing of the surface, as is seen at Rauch's gravel pit at Bethlehem. The fresh fragments firally reached the terminal deposits, and were mixed with the older weathered stuff; but were stirred up with it and are found at all depths, as on the crest of the ridge behind South Bethlehem, where in a rotten, unstratified deposit of great thickness, a fresh Calciferous bowlder lies near an equally fresh Lower Subcarboniferous cobble, on rotten gneiss, and under rotten and angular fragments of Potsdam. When a retreat of the ice took place, and a halt was made at a distance in the rear, the accumulations are generally of fresh fragments, and the thoroughly eroded surfaces show an abundance of groovings and striations. Those who see in this last all the work of glaciation, are unfortunate, in that they accept an incomplete sub-stage of the work for its entirety. Secondary advances to the former limits of glaciation frequently fail to remove portions of the former deposits, and cap them with a mass of fresh