Geology and Mineralogy. 395 



of the Yellvilie formation. The breeciation is believed to be 

 due to pressure induced at the time of the folding in the Ouachita 

 Mountain Ranges. Movements which resulted in folding and 

 thrust-faulting in the Ouachita Mountains and open folding in 

 the Arkansas Valley region are represented in the southern por- 

 tion of the Ozark district by breeciation, of individual beds with- 

 out disturbing their horizontal position. 



A Geological Reconnaissance across the Bitterroot 

 Range and Clearwater Mountains in Montana and Idaho; 

 by Waldemar Lindgren. 116 pp. 15 pis. 8 figs. Professional 

 Paper No. 27. — The Bitterroot Valley is one of the most striking 

 typographic features in the western part of the United States. It 

 is two to nine miles broad, runs almost exactly north and south, 

 and is depressed 5,000 feet below the deeply incised Bitterroot 

 Range to the west. The structure of this valley and of the 

 adjoining mountains has been worked out by Mr. Lindgren, and 

 shows some remarkable and unique facts. The depression owes 

 its existence to the normal fault, but the essential feature of this 

 dislocation is the fact that the fault plane corresponds with the 

 schistosity and jointing, so that there is every gradation between 

 the molecular and molar motions, indicating that both result 

 from the same forces. In the sheared zone there is " intimate 

 and inseparable relation between schistosity and faulting." The 

 striated slipping planes of the granite-schists are closely massed, 

 as many as twelve of them sometimes occurring in a thickness of 

 one inch. This locality would seem to be an excellent one to 

 test the divergent views regarding schistosity and jointing. Mr. 

 Lindgren thinks that the observations of the Bitterroot Range 

 confirm the opinions of Mr. G. F. Becker : that there is no essen- 

 tial difference between jointing cleavage and schistosity, that 

 they may both be produced at the same time, and that molecu- 

 lar movement is not necessarily confined to the zone of flowage. 

 The Bitterroot Range forms one of the largest glacial areas 

 known in the Cordilleras. Excellent illustrations of XT-shaped val- 

 leys, cirques, and various glacial deposits occur throughout the 

 Range. 



2. Baraboo Tron-beari?ig District, Wisconsin ; by Samuel 

 Weidman. Wis. Geol. and Nat. History Survey, Bull. No. 13, 1 71 

 pp., 23 pis., 3 figs. The Baraboo district, Wisconsin, shows an inter- 

 esting geological series, consisting of pre-Cambrian igneous and 

 pre-Cambrian sedimentary and of Paleozoic strata. The iron ore 

 is hematite developed from original limonite, and it is an interesting 

 fact that the ores showed no surface outcrop but were found by drill- 

 ing through sandstone and drift. In order to get at the iron ore 

 it was necessary to understand the geological structure of the pre- 

 Cambrian quartzite (Baraboo). A detailed study of the quartzite 

 shows that its structure consists of a double syncline, on the top 

 of which is deposited unconformably Potsdam sandstone. The 

 hypotheses of Irving, and later of Salisbury, are shown not to be 

 in accordance with the facts. 



