June 4, 1897.] 



SCIENGE. 



887 



one, but it contains about 3,000 feet of Carbon- 

 iferous deposits. To the westward is the anti- 

 clinal region of Devonian rocks which underlie 

 the characteristic glade country about Oakland, 

 Mountain Lake Park and Deer Park. West of 

 Oakland is another synclinal basin, containing 

 about 2,500 feet of Carboniferous beds. 



The geologic classification does not diifer ma- 

 terially from that outlined by W. B. Rogers and 

 others, but geographic names have been applied 

 to all of the formations. The lowest members 

 are a series of sandstones and quartzites, which 

 have been referred to as No. IV. and 'Medina.' 

 This series has been subdivided into the 

 Juniata formation, consisting of brownish-red 

 sandstones and shales ; the Tuscarora quartz- 

 ite, and the Cacapon sandstones, consisting 

 of thin-bedded red sandstones. Next there is 

 the representative Clinton formation, which 

 has been designated the Rockwood formation, 

 as in other folios ; the Lewistown limestones, in- 

 cluding representatives of the Helderberg and 

 associated limestones, and the Monterey sand- 

 stones, Romney shales, Jennings formation and 

 Hampshire formation, representing the Devo- 

 nian deposits. As the last three formations are 

 not sharply separated from one another, the pat- 

 terns by which they are represented on the map 

 are merged in a narrow zone along their boun- 

 daries. The Carboniferous period is represented 

 by the Pocono sandstone ; the Greenbrier lime- 

 stone ; the Canaan formation, which in a general 

 way is a representative of the Mauch Chunk 

 shales ; the Blackwater formation, which repre- 

 sents the Pottsville conglomerate in greater or 

 less part ; the Savage formation and Bayard 

 formation, which are the Lower Coal Meas- 

 ures ; the Fairfax formation, or Lower Barren 

 Measures, and the lOlk Garden formation, a part 

 of the Upper Coal Measures. 



The principal coal beds are in the Savage for- 

 mation, containing the ' six foot ' or Davis coal 

 bed ; the Bayard formation, containing the coal 

 bed known as the 'four-foot,' or ' three-foot, ' 

 or 'Bayard,' or 'Thomas' coal, and the Elk 

 Garden formation, containing the 'fourteen- 

 foot ' coal bed. 



On the economic sheet of this folio the coal- 

 bearing formations are strongly emphasized, and 

 underground contours are introduced to show 



the lay of the ' six-foot ' coal bed in the Savage 

 formation for each 100 feet. Other economic 

 resources of the area are red hematite iron ores 

 in thin beds in Rockwood shales and limestones 

 at several horizons, of which the lower member 

 in the Lewistown is locally available for cement. 



Folio 29, Nevada City Special, California, 1S96. 



This folio, by Waldemar Lindgren, consists 

 of seven pages of text, three special topographic 

 maps (scale 1:14,400) — the Grass Valley, Ne- 

 vada City and Banner Hill — three correspond- 

 ing maps showing the economic geology, and 

 three others giving structure sections. 



These maps, on a scale of about four inches 

 to the mile, have been prepared to illustrate the 

 detailed structure of the gold-mining regions in 

 the vicinity of Nevada City and Grass Valley. 

 Each of them comprises an area three miles wide 

 by four miles long, the total area being nearly 

 thirty-six square miles. The Nevada City and 

 Grass Valley areas fall within the boundaries of 

 the Smartsville atlas sheet, while the larger 

 part of the Banner Hill area falls within those 

 of the Colfax atlas sheet. The relief is that 

 common to the middle foothill region of the 

 Sierra Nevada — that is, the surface is a very ir- 

 regular and undulating plateau, deeply trenched 

 by the canyons of the recent river systems. 



Sedimentary rocks, chiefly referred to the 

 Calaveras formation, occupy small, usually nar- 

 row and long areas imbedded in the predomi- 

 nating igneous masses. Granodiorite occupies 

 a large part of the Nevada City and Banner 

 Hill districts, while a small massif of the same 

 rock is found in the Grass Valley district. 

 Large areas of diabase, porphyrite and brecci- 

 ated forms of these rocks surround and sepa- 

 rate the granodiorite areas. In the southwest- 

 ern part of the Nevada City district and the 

 northeastern part of the Grass Valley a large 

 and complicated massif is found, consisting in 

 part of diorite, in part of gabbro, pyroxenite 

 and serpentine. 



The slates of the Calaveras formation are the 

 oldest rocks. Next younger are the diorities, 

 gabbros and serpentines. Still later are the 

 diabases and porphyrites, and the intrusion of 

 granodiorite closes the succession of igneous 

 rocks. 



