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bulletin: museum of comparative zoology. 



two thousand five hundred feet in height, lay close to the verge of 

 an almost vertical precipice from one thousand to one thousand two 

 hundred feet high. Below this a series of lesser cliffs, separated by 

 steeply sloping screes of rock-waste stepped downward to the uneven 

 floor of a deep N. E.-S. W. valley. On the southeast the valley is 

 hounded by a similar arrangement of cliffs and taluses. It ends as a 

 great cul-de-sac two miles in length in a thousand-foot head-wall over 

 which there cascades a large brook. 



Figure 1.— Dissected plateau of Mugford sedimentary series, viewed from Mugford 

 Tickle. Each of the two summit knobs was estimated to be about 2500 feet in elevation. 

 Looking north. Drawn from a photograph. Heavy black line represents upper surface 

 of the basement Complex. 



On landing, we found that the first and natural impression, that this 

 systematic array of scarps and taluses signified a stratified structure for 

 the massif, was justified (Fig. 1 and Plate 11). At the foot of the great 

 slope the basement of all the other rocks is represented in an irregular 

 floor of contorted and faulted gneisses and amphibolites. The surface of 

 the familiar complex appears at all elevations above the sea up to about 

 six hundred feet. Next above the light colored zone of the schists comes 

 a series of black slates fifty to one hundred feet thick, indurated at the 

 contact by a conformable three hundred-foot sheet of apparently intrusive 

 diabase. The edge of this sheet forms one of the lowest strong cliffs 

 above the basement. The diabase in its turn is overlain by a great thick- 

 ness of slates, quartzites, sandstones, quartz breccias, volcanic agglomer- 

 ates, and trap layers. The inaccessibility of the cliffs and the shortness 

 of the time allowed for examination rendered it impossible to determine 

 the absolute strength of the various members. The enormous size and 

 number of the blocks found in the screes seemed to show that the greater 



