January 21, 1898.] 



SCIENCE. 



81 



blance to the Keweenawan eruptives of the 

 Lake Superior region. They possess con- 

 siderable petrographical interest. 



Analyses which were given showed them 

 to be rich in soda and of a composition that 

 would lead one to infer the presence of nephe- 

 line, yet none could be detected by chemical 

 or optical tests. The rocks attracted much 

 interest from the petrographers present. 



In discussion J. F. Kemp outlined briefly 

 the area in the Champlain Valley in which 

 the smaller dikes were found, stating that 

 they practically ceased near Ticonderoga 

 and were not known in the southwestern 

 Adirondacks. J. P. Iddings mentioned 

 the difficulty of giving an expressive name 

 to the rocks and the curious position that 

 they occupied. 



Clastic Huronian Rocks of Western Ontario, 



and the Relation of Huronian to Laurentian. 



A. P. Coleman, Toronto, Canada. 



The speaker had been led to observe and 

 study the rocks in question while reporting 

 on the gold districts north of Lake Superior 

 for the Ontario government. He reviewed 

 the work of Lawson, H. L. Smj-th and 

 others in connection with maps, and de- 

 scribed especially the clastic rocks. The 

 distribution of the Conchiching around 

 dome-like areas of the Laurentian crystal- 

 lines, he suggested, could be perhaps ex- 

 plained by dome-like upheavals or bulgings 

 of the latter, the domes being located where 

 the overlying burden of sediments was thin- 

 nest. It was suggested that the same ex- 

 planation might be applied to mountains 

 elsewhere. 



In discussion Robert Bell reviewed the 

 early work of the pioneer observers in the 

 region, and differed from Professor Cole- 

 man in his interpretation. G. O. Smith 

 stated that many contacts in the Huronian 

 regions on the south were obscure, but that 

 others were very plain and showed a basal 

 conglomerate resting on the ancient granite. 



G. M. Dawson spoke of the importance and 

 difiSculty of discriminating between an in- 

 truded batholite and a supporting basement 

 of older granite. A. E. Barlow briefly de- 

 scribed the breccias, graywackes, quartzites 

 and conglomerates on Lake Temiscaming, 

 and insisted that Laurentian was now only 

 a petrographical and not a time-term. In 

 closing the discussion Dr. Coleman replied 

 in a few words to the remarks that had 

 been made. 



The Grading of Mountain Slopes. W. M. 



Davis, Cambridge, Mass. 



With the lantern Professor Davis threw 

 on the screen a series of views of slopes in 

 various mountain ranges and from areas of 

 other topographic forms and brought out 

 the idea that, unless sapping or some other 

 undermining action is in progress, the sur- 

 face reaches a slope or grade that expresses 

 the balance established between the weath- 

 ering forces and the resistance of the ma- 

 terials. This feature is quite pronounced 

 and characteristic and is described by 

 speaking of the slopes as 'graded.' The 

 grades differ according to the materials in- 

 volved, and the evenness of the ' grade ' is 

 largely a function of the time of exposure. 



Tlie Harvard Geographical Models. "W. M. 



Davis, Cambridge, Mass. 



The Harvard Geographical Models, de- 

 signed by the author and constructed by 

 Mr. G. C. Curtis, have been prepared for 

 the purpose of giving systematic illustra- 

 tion of a number of geographical forms in 

 their genetic relationship. Three of the 

 series were described and exhibited by 

 means of lantern slides. They represent a 

 mountainous region descending to the sea ; 

 the same after depresssion, whereby the 

 shore-line has become very irregular ; the 

 same after elevation, whereby a coastal 

 plain has been added to the land area. 



The Society then adjourned until the fol- 

 lowing day. In the evening a reception 



