188 



SCIENCE 



[N. S. Vol. XXXII. No. 814 



mechanieal effect is lost in the cushion of water 

 below the falls, which thereby balances any lesser 

 efficiency of the smaller falls, which strike directly 

 on the talus below. In the variable energy, the 

 power of deepening the pool beneath a waterfall 

 seems to act as a mean balancing medium, so that 

 there is found no reason for deviating from the 

 laws of erosion in the changes at Niagara, until 

 some unexpected discovery shall be made. So far, 

 the author has been unable to find any grounds 

 based upon observation, for greater variation in 

 the approximate age of Niagara than those pro 

 vided for. 



Natural Bridges of 'North America mth a Dis 

 cussion of Their Origin: Heed man F. Cleland, 

 Williamstown, JIass. 



A. Natural bridges initiated by stream erosion 



1. By the perforation of the neck of an incised 



meander. 



2. By pot-hole action. 



3. By erosion assisted by frost action. (Yellow- 



stone.) 



4. Travertine-cemented stream deposits under- 



cut by stream action. 



5. By the undercutting of a petrified log. 



6. By the headward cutting of two streams. 



B. Bridges initiated by wave erosion. 

 1. Certain wave-cut arches. 



C. Bridges initiated by solution. 



1. By seepage through a joint or other crack, 



thence along a bedding plane and dis- 

 charging under a fall or rapid. 



2. Caving in of the roof of a cavern. 



D. Bridges formed by gravity. 



1. A stone wedged in a narrow chasm. 



2. A slab separated from one bank and fallen 



over to the other. 



E. Bridges formed by deposition. 



1. Snow and ice bridges. 



2. Travertine bridges and bridges formed by the 



cementation of stream bowlders which 

 have afterwards been partly cut through 

 by erosion. 

 Summary: 



1. Character of rock in which bridges occur. 



2. Stage of development of the region in which 



they occur. 



3. In glaciated and non-glaciated regions. 



4. Summary of origin. 



Discussed by H. C. Hovey and J. W. Spencer. 

 Geological Suggestions Derived from a New Ar- 

 rangement of the Elements: B. K. Emerson, 

 Amherst, Mass. 

 The elements were arranged in the order of the 



octave, two octaves and four double octaves, and 

 interesting physical and geological relations were 

 brought out. 



New Light on the Geology of the Wasatch Uourtr 

 tains: Eliot Blackweldeb, Madison, Wis. 

 The past season's work of the U. S. Geological 

 Survey in the Wasatch and Bear River Ranges of 

 Utah, has added several facts of importance to the 

 current interpretation of the structure and stra- 

 tigraphy of the region. The Weber quartzite thins 

 rapidly north and northwest of the type locality 

 and there is evidence indicating that this thinning 

 has been caused by erosion during the Pennsyl- 

 vanian period. The Ogden quartzite appears to be 

 neither Devonian, as first reported, nor Ordo- 

 vician, as stated in more recent years, but merely 

 a repetition of the lower Cambrian quartzite upon 

 a large overthrust. The great body of " Wasatch 

 quartzite " of the King Survey was found to be 

 separated from the known Cambrian quartzite by 

 a distinct although readily overlooked unconform- 

 ity. Structurally the Wasatch range proves to be 

 more than a simple monocline with local folds. 

 Near Ogden there are several large overthrusts 

 and a number of subsequent transverse normal 

 faults, one of which has an unusually large dis- 

 placement. 



Discussed by S. F. Emmons, Bailey Willis, A. 

 W. Grabau, Arthur Keith and the author. 



Hawaiian Volcanoes: Reginald A. Daly, Boston, 



Mass. 



Evidence was given for the view that the vent 

 at Kilauea is an opening in the roof of a large 

 laccolith. This conception offers a tentative ex- 

 planation of the observed independence of Hale- 

 maumau and Mokuaweoweo (Mauna Loa). A 

 small, visible laccolith on Hawaii was then de- 

 scribed. The paper also included a discussion of 

 (a) the method by w-hich the heat is maintained 

 in Halemaumau; (6) the differentiation of Maima 

 Kea alkaline rocks from basaltic magma; and 

 (c) the development of Mauna Kea in its present 

 form. 



Discussed by T. A. Jaggar, Jr. 



Genetic Classification of Active Volcanoes: T. A. 



Jaggab, Jr., Boston, Mass. 



The author has studied seven active volcanoes 

 in last eight years. Mercalli's classification by 

 types of eruption and kinds of lavas is not genetic 

 and hence contains many overlaps. Volcanoes 

 show kinship of origin and stages of growth 

 related to a common origin. It is believed that 

 a classification based on (1) the unity of all 



