390 



SCIENCE 



[N. S. Vol. XXV. No. 636 



not produced, and their identification was 

 accomplished by determining their physical 

 properties — optical characteristics, specific 

 gravity, hardness, etc. 



The conditions of formation of each of these 

 four forms were described, and attention 

 called to the stability of the monoelinic pyr- 

 oxene form at all temperatures — ^the other 

 forms bearing monotropic relations to this 

 form. Above 1,250° both artificial and nat- 

 ural enstatite change into the monoelinic 

 pyroxene with evolution of heat. The stable 

 form melts at 1,521°. The experiments show 

 that temperature and viscosity are factors of 

 prime importance in the formation of unstable 

 bodies. Thus, from melts or from silicate 

 solutions, the stable monoelinic form of mag- 

 nesium metasilicate crystallizes at the highest 

 temperature, enstatite next, and the amphi- 

 boles probably lowest of all. From thin solu- 

 tions the stable form is obtained at still lower 

 temperatures, 800° to 1,000°, while from aque- 

 ous solutions at 375° to 4Y5° an amphibole 

 results. The intergrowths of enstatite with 

 the monoelinic pyroxene, and of the two am- 

 phiboles, which were obtained in close resem- 

 blance to those of nature, are cases of false 

 equilibrium, and their occurrence establishes 

 the fact that it can not be assumed that all 

 rocks or mineral aggregates are systems in 

 true equilibrium. The study of the enstatite 

 from the Bishopville meteorite indicates that 

 it must have cooled very rapidly from a high 

 initial temperature, and there is evidence that 

 the same is true of other meteorites. The 

 conditions of formation of the four forms of 

 magnesium metasilicate are in accord with 

 the mode of occurrence of the natural min- 

 erals of similar composition. 



Local Glaciation in Maine: Mr. Frederick G. 



Clapp. 



In various parts of Maine there are evi- 

 dences of local valley glaciers of post- Wiscon- 

 sin or late Wisconsin age. These are most 

 pronounced in the vicinity of Mt. Katahdin. 

 Several valleys in the northern slopes of that 

 mountain are shown by the position of mo- 

 raines to have been occupied by glaciers, and 

 more extensive evidences are found through- 



out the region southeast of the mountain. 

 The indications consist chiefly in the existence 

 of nimierous moraines formed entirely of large 

 granite boulders of the character of granite 

 found only on Mount Katahdin. As the di- 

 rection of glacial striae in northeastern Maine 

 is directly south, and as the granite moraines 

 are found both south and southeast of the 

 mountain, the material is shown to have been 

 deposited by glaciers of post- Wisconsin or late 

 Wisconsin age moving outward and south or 

 southeastward from Mount Katahdin as a 

 local center. Further indications are fur- 

 nished by the depth of weathering in some of 

 the more sandy moraines situated farther 

 from the mountain. The glaciers extended at 

 least twenty miles from the mountain. Eef- 

 erences were cited of descriptions of similar 

 local glaciers in the White Mountains of New 

 Hampshire, the Green Mountains of Vermont 

 and the Katskill Mountains of New Tork. 

 The Late History of the Lower Colorado 



River: Mr. W. T. Lee. 



The paper dealt mainly with the geographic 

 and geologic features of the Colorado Valley 

 from the mouth of the Grand Canyon to the 

 Gulf of California. It was shovsm that the 

 data, principally physiographic, warranted a 

 subdivision of Tertiary and Quaternary time 

 into epochs, the sequence of which is appar- 

 ently clear, as announced by the speaker ia. 

 the Bulletin of the Geological Society of 

 America for 1906. Briefly stated, these epochs 

 are as follows, given in order from youngest 

 to oldest. 



1. Sedimentation — formation of flood plains. 



2. Erosion — during which the river cut 

 through the Chemehuevis gravels. 



3. Sedimentation — accumulation of about 

 YOO feet of sands and gravels which extend 

 from the Grand Canyon to the Gulf of Cali- 

 fornia and are known as Chemehuevis gravels. 



4. Erosion — diversion of the river from its 

 former course in Detrital-Sacramento Valley 

 to its present course west of the Black Range, 

 and the cutting of Boulder, Black, Mohave 

 and Aubrey canyons to a depth of 2,000 feet 

 or uiore. 



5. Sedimentation — ^wide-spread aggradation 

 over the basin region. Deposition by the 



