126 



SCIENCE 



[N. S. Vol. XXX. No. 760 



and stability of all the mixtures which result 

 when one of the components is present in excess 

 of the exact proportion required to form the min- 

 eral, establishes the practicability and effective- 

 ness of physico-chemical methods in solving such 

 questions as the order of crystallization from the 

 magma and the stability of the crystalline prod- 

 ucts formed during the cooling to present tem- 

 peratures. The relations between these minerals 

 are nearly all eutectic, and when considered in 

 connection with previous work on isomorphous 

 mixtures, serve to illustrate the certainty with 

 which such measurements upon rock-making min- 

 erals can be made and interpreted, their freedom 

 from dependence on the personal judgment of the 

 observer, the comprehensive way in which char- 

 acteristic differences of physical form, as well as 

 those of chemical composition, are taken into 

 account, and the ready adaptability of the system 

 to provide a more comprehensive classification of 

 the mineral relations whenever a sufficient body 

 of such measured data shall have been gathered. 



The scope of the laboratory problem, that is, 

 the immense domain within which these methods 

 have now been successfully applied, is shown by 

 the fact that these minerals were studied not only 

 through all percentages of the components, but 

 over the entire range of temperatures in which 

 stable forms occur, either in the mineral com- 

 pounds or their components — in all, a range of 

 about 2,100 centigrade degrees. 



Pure silica was found to possess three stable 

 crystal forms : ( 1 ) a-quartz — stable at ordinary 

 temperatures and up to 575° C. ; (2) /3-quartz — 

 stable from 575° to 800°; (3) tridymite (cristo- 

 balite) — stable from 800° to the melting tempera- 

 ture (1,600°). 



Pure lime has but one form which melts in 

 the electric arc but is out of reach of accurate 

 pyrometry. 



Lime and silica combine to form two com- 

 pounds: (1) The metasilicate — ^^vhich exists in 

 two stable crystal forms : (a) WoUastonite, stable 

 at ordinary temperatures and up to 1,190° C. ; 

 (6) pseudo-wollastonite, stable from 1,190° to its 

 melting point, 1,512°. (2) The orthosilicate — 

 with three stable crystal forms which were desig- 

 nated for convenience: a, stable from 1,410° to 

 the melting temperature, 2,080° ; ;8, stable from 

 675° to 1,410° ; 7, stable at ordinary temperatures 

 and up to 675°. 



The metasilicate of lime combines with the 

 metasilicate of magnesia — possessing two stable 

 and three unstable crystal forms, of which one 



(unstable) corresponds to enstatite — to form only 

 one mineral, diopside, stable at all temperatures 

 up to its melting point, 1,395°. 



The measurements were made at constant (at- 

 mospheric) pressure and in the absence of water. 



The measurements themselves depend upon: 

 (1) the chemical purity of the component min- 

 erals; (2) the ability to establish equilibrium 

 between them at the temperatures where the char- 

 acteristic changes occur within the time available 

 for a laboratory experiment; (3) sufficiently sen- 

 sitive and accurate temperature measuring devices 

 to locate with certainty every characteristic 

 change in the energy content of the system. 

 The Slumgullion MudFlcno: Mr. Whitman Cross. 



The Slumgullion mud flow is a landslide of un- 

 usual character, which took place many years ago 

 in an eastern tributary of the Lake Fork of Gun- 

 nison River a few miles above Lake City, Colo. 

 The damming of the Lake Fork by this flow 

 caused Lake San Cristobal, a sheet of water two 

 miles long. 



The flow originated at the south end of a high 

 ridge at the head of a minor branch of the Slum- 

 gullion drainage. From this point, with an ele- 

 vation of about 11,500 feet, the flow descended 

 2,500 feet to the valley of the Lake Fork, four 

 miles distant from the source. The material of 

 the flow now fills the valleys in which it lies to a 

 probable elevation of 150 to 300 feet above the 

 original bottom. 



The topographic features of the flow are very 

 pronounced. It is bounded for nearly its entire 

 length by two moraine-like lateral ridges of very 

 sharp outline. Between these the flow is usually 

 lower and characterized by furrows and trenches, 

 knolls and hollows of confused relations resem- 

 bling those of modified landslide areas or of some 

 glacial deposits. 



The material of the flow is mainly a soft, light 

 yellow or nearly white decomposition product of 

 pyroxene andesitic lava and irregular fragments 

 of the same rocks, some of which are fresh, while 

 more are partly altered. The origin of the flow is 

 intimately connected with this decomposed condi- 

 tion of the andesite at its head. It appears that 

 at the end of the ridge mentioned a large mass of 

 andesite belonging to a complex of flows was ex- 

 tensively decomposed, the product consisting prin- 

 cipally of opaline silica, hydroxides of iron and 

 alumina and gypsum, forming a soft mealy mass 

 which on saturation with water became a liquid 

 mud. On this mass rested less altered beds of 

 andesite. 



