83. Lower Narrows of Baraboo River, from near contact with Archæan quartzite.

A much indurated, fine-grained sandstone carrying quartzite pebbles. The quartz fragments, originally but little rounded, are all strongly enlarged, so that there is a considerable degree of interlocking. There is also present some fine independently deposited interstitial quartz. The section does not differ materially from those of many Archæan quartzites. (Slide 742.)

84. Roche Écrit, Adams County, Wisconsin.

A dark-purplish, in places very much indurated sandstone. The grains are all enlarged, and occasionally have crystal faces developed. (Slide 749.)

85. Packwaukee, Marquette County, Wisconsin.

A pale, buff-colored, much indurated sandstone, showing only very rare crystalline facets. In the thin section the grains are seen to have been enlarged slightly, so as to fit closely without any dovetailing. Occasionally the enlargements have had an opportunity to develop crystal faces. (Slides 731, 732.)

86. Black River Falls, Jackson County, Wisconsin.

A white, rather coarse-grained rock, not so much indurated as the last-described, and showing more crystal facets, although not very plentifully. The thin section is much like that of the rock last described, except that the enlargements are proportionally broader and have more often developed crystal faces. (Slides 733, 734.) 87. New Lisbon, Wisconsin.

A fine-grained, pink-and-white-mottled sandstone, from which the light is reflected in numerous sparkling points. The induration, while distinct, is only slight, small fragments crumbling readily in the fingers. The crumbled sand mounted in balsam shows every grain enlarged, the lines of junction between the old and new quartz being always strongly marked. The enlargements have in all cases developed crystalline faces, which are, however, only perfect and uninterrupted upon the smallest of the grains. In most cases they are more or less indented by the enlargements of contiguous grains. This rock may be taken as type of the crystal-faceted sandstones. (Slides 710 to 716 inclusive.) (See Figs. 4, 5, 6, Plate II.)

88. Middleton, Dane County, Wisconsin.

A fine-grained, loose, white sandstone, showing the grains sparkling from crystal facets. The balsam mounting of the sand crumbled from the rock shows the grains with the usual cores and crystal outlines. (Slides 1469, 1470.)

IN THE EASTERN SANDSTONE OF LAKE SUPERIOR.

89. West Branch of the Ontonagon River (Sec. 13, T. 46, R. 41 W., Michigan).

A reddish, coarse-grained, indurated sandstone. The quartz fragments which make up the rock have all been enlarged, sometimes very much so, so as to interlock. There is also some independently oriented fine interstitial quartz. Some much reddened, feldspathic detritus is included. (Slides 95, 96, 97.)

90. Quarry on Torch Lake Railroad, Keweenaw Point, Michigan.

A white to pinkish, feebly indurated quartzose sandstone. Some of the less indurated portions show numbers of faceted grains. The slide here described is from one of these less indurated portions. It is seen to be made up almost entirely of much rolled quartz fragments, which have in nearly every instance been enlarged, the enlargements only occasionally showing crystalline outlines. These crystal outlines

are, however, more frequently to be seen in the balsam mounting of crumbled sand. They are not nearly so numerous, however, as in some of the rocks previously described, the grains having interfered too much to form crystal outlines. The outlines of the original grains are usually very strongly marked by brownish iron oxide, There are occasional rounded fragments of feldspar present, and in each thin section may be seen a few particles worn from some of the fine-grained Keweenawan eruptives. (See Figs. 7, 8, 9, Plate II.) (Slides 513, 514, 1471, 1472, 1473.) See with regard to this rock also Copper-Bearing rocks of Lake Superior, pp. 356358. See also for an earlier description M. E. Wadsworth in Bull. Mus. Comp. Zool., Vol. VII, No. 1, p. 117. Wadsworth found the crystal-outlined grains abundantly in his sections, although we failed to do so in ours until recently. He regarded these crystal grains as being the usual dihexahedral crystals of quartz-porphyries, on which view the crystals antedate the formation of the sandstone instead of being subsequent to it. More recently (Science, Vol. II, No. 23, p. 52, July 13, 1883) he has reasserted this view. But a careful re-examination of this rock, as also of others from other places within the area of the Lake Superior sandstone, has served to convince us that in all of these cases, as in all sandstones yet examined by us, provided with such faceted grains, they owe their crystal faces to secondary enlargements of rolled fragments. It is of course possible and even probable that these quartz fragments were once, some of them, the quartzes of quartz porphyries, but if so they have rarely, if ever, retained their crystal faces, as it is, indeed, hardly conceivable that they should do.

91. Quarries at Marquette, Mich.

A reddish, fine-grained sandstone, showing numerous minute glistening flakes of mica. Quartz fragments make up rather more than half of the rock, many of the grains being finely complex. The simple quartz grains are mostly very angular; many of them show very distinct enlargements. The remainder of the rock is composed chiefly of fragments of feldspar, including othoclase and plagioclase, with chlorite, brown iron oxide, and muscovite flakes, the chlorite having resulted from the alteration of the feldspars. The plagioclase includes quite a number of large-sized pieces of microcline.

92. Near Rockland. South of the Trap Range (S. E. 1, Sec. 7, T. 50, R. 39 W., Michigan).

A fine-grained, feebly indurated, pinkish, quartzose sandstone, sparkling from presence of crystal facets, each quartz fragment being enlarged, the enlargements being often provided with crystalline outlines. (Slides 1475, 1476.)

IN THE WESTERN SANDSTONE of lake supERIOR.

93. Basswood Island, Ashland County, Wisconsin.

A fine-grained, feebly indurated, white sandstone, containing besides the quartz many feldspar fragments. The quartzes are often enlarged, the enlargements being in many cases supplied with crystal facets. (Slide 53, Wis. sur. series.)

SILURIAN ROCKS.

IN THE SAINT PETER'S SANDSTONE OF WISCONSIN.

94. Near Lancaster, Grant County, Wisconsin.

This rock is represented in our list only by slides kindly furnished by the Rev. A. A. Young, of New Lisbon, Wis. They are dry mountings of the sand crumbled by hand from the rock. The grains are furnished with crystal facets from secondary deposition.31 (Slides 707 to 711.)

31 Amer. Jour Sci., July, 1883.

95. Arlington Prairie, Columbia County, Wisconsin.

The Arlington Prairie is part of a large elevated area underlain by the Lower Magnesian Limestone, but dotting it here and there are small outliers of the Saint Peter's sandstone. A group of these outliers occurs in the southwestern part of the town of Arlington. Most of the rock of these outliers is quite loose, and of the ordinary character of the Saint Peter's sandstone. Along its weathered surface, however, and along the sides of joint cracks, it is very much indurated, becoming even a completely vitreous quartzite for the distance of one-fourth or one-half an inch inwards from the surface. Sections of this completely vitrified portion show the quartz fragments with enlargements that everywhere fit closely together or interlock, but sections taken from an inch or two below this crust show the enlargements frequently furnished with crystal facets, the enlargements having interfered with one another sufficiently to give a slight induration. Fig. 1, Plate III, shows the appearance of a thin section of this less indurated portion as seen in the ordinary light.33 (Slide 724). 96. Gibraltar Bluff, Columbia County, Wisconsin.

A very much indurated, fine-grained rock, in which a fine arenaceous texture is visible only upon the closest inspection. The rock is one which, if found among the crystalline schists, would undoubtedly be classed as a true quartzite, and the appearance of the thin section would entirely bear out this classification. It is made up only of interlocking grains of quartz of two very different sizes, the larger ones predominating. The large ones of these areas, and many of the smaller ones, show each a more or less plainly outlined fragmental nucleus. The areas interlock, often very intricately, and in every possible sense the rock is fully as “metamorphic” as any quartzite yet studied from the Archæan formations, and yet it is a mere local phase wholly independent of any igneous or other apparent metamorphosing action, in a formation whose ordinary character is that of an incoherent sandstone. In no Archæan quartzite that we have examined is the interlocking of the quartz areas, and the consequent appearance of complete original crystallization, more marked than in this sandstone. See Fig. 1, Pl. V. (Slide 727.)

97. Eureka, Nevada.

IN THE EUREKA QUARTZITE of nevada.

This rock and the three following are the ones in which Hague and Iddings noted enlargements of quartz grains as long ago as the summer of 1881. They will be found fully described in Hague's monograph upon the Eureka district. Mr. Hague has been kind enough to furnish us specimens and slides for the purpose of comparing them with quartzites which we had examined. The specimen of Eureka quartzite furnished by Mr. Hague would be classed by us as a semi-vitreous quartzite. The enlargements of the quartz fragments of which the rock is composed has produced close fitting but never any considerable interlocking. But still the rock is fully as much altered as any of the true Huronian quartzites.

DEVONIAN.

98. Sandstone from the White Pine shale, Eureka, Nevada.

A fine-grained, strongly indurated sandstone, composed of fragments of quartz and of chalcedonic or amorphous silica. The quartz fragments are often enlarged and are sometimes furnished with crystal faces. (Slide 1436.)

32 Geol. of Wis., vol. II, p. 583.

For figures drawn from the vitrified crust of this rock see Amer. Jour. Sci., June, 1883, p. 407.

31 Amer. Jour. Sci., June, 1883, p. 408.

CARBONIFEROUS.

99. Eureka, Nevada, Diamond Peak quartzite.

A fine-grained, greenish-drab, feldspathic quartzite. In the thin section feldspar, often much altered, is seen to compose a large proportion of the rock. The minute grains of quartz show relatively wide enlargements. (Slide 1368.)

100. Henry Mountains, Utah.

TRIASSIC.

A light-gray to pinkish, fine-grained, feebly indurated sandstone from near contact with one of the laccolites. Small rounded grains of quartz compose the larger part of the rock. These have often been enlarged, and the enlargements fit somewhat closely. There are some grains of feldspar and, interstitially, calcite, fine quartz, clayey material, and iron oxide. (Slide 1367.)

CRETACEOUS.

101. Courtlandt, Nicollet County, Minnesota.

A light-gray, compact, calcareous sandstone, consisting of quartz fragments embedded in a matrix of crystalline calcite. The quartz fragments, only rarely in contact with each other, have quite often been enlarged. (Slide 1384.)

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II.

ENLARGEMENTS OF FELDSPAR FRAGMENTS IN CERTAIN KEWEENAWAN SANDSTONES.

BY C. R. VAN HISE.

For some time past I have been on the outlook for evidence of the secondary enlargement of feldspar fragments. In the slate conglomerates of the north shore of Lake Huron (as mentioned in Part I of this bulletin) I have found what may be enlarged feldspar grains, but the evidence is not sufficiently satisfactory that any of the material is of secondary origin, the lines of separation between the supposed new material and the nuclei being illy marked. However, I have found what seem to be additions to grains of that mineral in certain of the Keweenawan feldspathic sandstones. The specimens in which the supposed enlargements were first found are taken from those portions of the sandstones almost in contact with overlying basic eruptives. This position is evidently a favorable one for the development of such enlargements, the heated alkaline waters which would naturally descend supplying appropriate conditions. Then, too, quartz enlargements, when most easily found, are shown by lines of ferrite about the nuclei, and are ordinarily best seen in the less indurated quartzites. The Keweenawan sandstones are highly ferruginous, and are of an open texture; hence, if in them the feldspar fragments have taken new growths, the conditions for their detection are favorable.

The feldspathic sandstone immediately underlying the diabase of Eagle Harbor, Michigan, is of a uniform medium grain, a magnifying glass showing but little quartz. The feldspar grains are stained red with iron oxide. Hydrochloric acid gives with the powder a slight effervescence. In the thin section the sandstone is seen to be composed largely of grains of different feldspars, next to which in abundance are rounded complex fragments derived from a granitic porphyry,' consisting of feldspars penetrated by a saturating quartz. Then follow in order of abundance complex fragments of some altered basic rocks. Finally, a few grains of quartz and a little secondary calcite are noted. The feldspars are frequently somewhat kaolinized, but most of the grains are fresh enough to give quite uniform colors in polarized light, and, in the cases of the plagioclases, well defined twinning bands. The grains are all rounded, their boundaries being broad lines of ferrite. However, some subsequent mineral has used these grains as nuclei 'Third Annual Report U. S. Geol. Survey, p. 114.