994 



SCIENCE. 



[N. S. Vol. XII. No. 313. 



large class of the drift formations shows 

 modification by the waters of the melting 

 ice surface and of rains, and is, therefore, 

 called modified drift. These several phases 

 of actioQ and resulting deposits of the ice- 

 sheet are discussed in the full paper, with 

 illustrations from field observations, and 

 from comparison with now existing glaciers 

 and ice-sheets. 



Professor C. W. Hall, in a paper on 

 ' The Chengwatona Series of the Keweena- 

 wan ' formation, describes this interesting 

 series of volcanic rocks, first identified by 

 Chamberlin as belonging to the Lake Supe- 

 rior copper-bearing formation. These rocks 

 are exposed along the Snake River almost 

 continuously for two miles, with edges 3 to 

 20 feet above the stream. The succession 

 consists of basic eruptions (lava flows of 

 typical structure) with intercalated con- 

 glomerates. The bottom of each flow is of 

 very fine texture and in places apparently 

 devitrified ; the middle portion is of coarser 

 yet quite uniform texture, while the top is 

 strongly amygdaloidal with frequent tufia- 

 ceous phases. The recognition of the difier- 

 ent phases of each flow and the transition 

 from one flow to another can be distinctly 

 seen, as the division planes are sharply 

 drawn . In two or three instances the over- 

 lying tuff is thicker than the compact por- 

 tion of the flow. The diabase is, for the 

 most part, of the characteristic ophitic 

 type, exposed surfaces first mottling and 

 then becoming pitted through unequal de- 

 composition. The amygdaloid carries the 

 minerals characteristic of the Lake Supe- 

 rior basic eruptives with laumonite or some 

 relative the predominant one. Lying in- 

 terbedded with these diabase flows is a 

 series of conglomerate beds; five were 

 counted. They vary in thickness from 5 

 feet to 104 feet, and represent a total of 

 more than 200 feet. Pebbles of gabbro, 

 diabase, diabase porphyry, augite syenite 

 and granite conglomerate are recognized. 



thus suggesting an age even later than tha 

 of the augite syenite around Duluth, in 

 other words, high up in the Keweenawan 

 formation. The number of successive lava 

 flows in the Chengwatona series is its most 

 remarkable feature ; not less than 45 were 

 counted, and neither the top nor bottom 

 flow was seen. The total thickness cannot 

 be less than 10,000 feet actually in sight. 

 The attitude of the entire series is uniform, 

 and there is no sign throughout of suflBcient 

 displacement to duplicate a single flow. 

 Besides, the conglomerate beds are so un- 

 like in thickness that they cannot by error 

 well be duplicated in the above estimate. 



In a paper on ' A Simple Modeling Ma- 

 chine,' Dr. E. B. Mathews described a 

 simple machine, designed by himself, of 

 which many geologists and geographers 

 have long felt a need. 



The expense and great amount of time 

 required to make simple relief models of 

 areas studied by the existing methods have 

 prevented geologists from making use of 

 models in the representation of tentative 

 geological interpretations. Moreover, the 

 models made by cross sections, pegs or 

 layer methods take much time and involve 

 a high degree of personal equation in the 

 sculpture. The machine described is a me- 

 chanical device for representing with con- 

 siderable accuracy the territory' included 

 within a topographic atlas sheet. Two fea- 

 tures are regarded of special importance : 

 in such a machine, there must be rigidity 

 in the horizontal plane in order to avoid 

 distortion, and even greater rigidity in the 

 vertical plane to eliminate vertical exag- 

 geration. It was found possible to obtain 

 the first by the use of a rigid pantograph in 

 which the arms were about an inch and a half 

 broad and three-eighths of an inch thick. 

 The vertical accuracy is obtained by a stylus 

 passing through the end of one arm of the 

 pantograph and held at the desired height 

 by two set screws, the whole resting on a 



