MOUNT GEEYLOOK. 137 



trace of stratification can be detected. As the cleavage foliation in some 

 places coincides with the stratification foliation both in strike and dip, in 

 others agrees in strike while differing in angle of dip, and in still others 

 differs from it in the direction of both strike and dip, and, furthermore, as 

 the marks of stratification are not infrequently subject to purely local 

 changes, the whole matter is attended with much difficulty. This is enhanced 

 by the absence of all outcrops over considerable areas. Satisfactory results 

 can be reached only by accumulating a great number of observations, 

 rejecting those which appear in the least doubtful, and by closely studying 

 the relations of the remainder. As a rule, the most reliable structural data 

 on Grevlock have been obtained from outcrops where two different beds were 

 in visible contact, or from a series of related outcrops in all of which both 

 cleavage and stratification foliations were equally manifest and discordant, or 

 else from large surfaces of rock at right angles to the strike, where the general 

 trend of the minor folds could be distinctly seen. 1 



1 The following list includes important recent works bearing on tbe subject of cleavage: 



Tbeodor Kjerulf: Om Stratiflkationens Spor (traces of stratification). Kristiania, September, 1877. 



A. Ileim : Mechanismus der Gebirgsbildung, im Anschluss an die geologische Monographic der 

 Toedi-Windgallen-Gruppe. Basel, 1878. 



A. Daubree: Etudes synthetiqiies de geologic experimentale. Paris, 1879. 



II. Clifton Sorby: On the structure and origin of noncalcareous stratified rocks. Quarterly 

 journal of the Geological Society of Loudon, vol. 36, 1880, p. 72. 



Ed. Jannettaz : Memoire sur les clivages des roches (schistosite, longrain.), et sur Ieur reproduc- 

 tion. Bulletin de la Societe Geologique de France, 3rd ser., vol. 12, 1884, p. 211. 



O. Fisher: On faulting, jointing, and cleavage. Geological Magazine, new series, decade 3, vol. 1, 

 p, 2(i:., 266, 396. London, 1881. 



A. llarker: On slaty cleavage and allied rock-structures, with special reference to the mechan- 

 ical theories of their origin. British Association Report. 1885(1881!), pp. 813-852. 



T. G. Bonney: On the mctamorphic rocks. Anniversary address. Quarterly Journal of tbe 

 Geological Society of London, vol. 12, p. 35. London, 1886. 



Hans Reusch : Geologische Beobachtungen in einem regional metamorphozirten Gebiet am Har 

 dangerfjord in Norwegen. Neucs Jahrbuch fur Min., Geol. u. Pal., V Beilage-Band, Heft I, p. 53. 

 Stuttgart, 1887. 



Emm. de Margerie & Dr. Albert Heim: Die Dislocatiouen der Erdrinde; Versuoh einer Definition 

 ■ i i i < 1 Bezeichnung. Zurich, 1888. 



Henry M. Cadell: Experiments in mountain building. Transactions of the Royal Society of 

 Edinburgh, vol. xxxv, part l, third series of experiments. Feb. 20, 1888. Abstract in Nature, vol. 

 37. p. 188. March 22, 1888. 



Hans Reusch : Bommelon og Karmpen med omgivelsei geologisk beskrevne. With an English sum- 

 mary of the contents. Kristiania, 1888. 



T. Nelson Hale: On plicated cleavage foliation. Am. Jour. Sci., ser. in, vol. 13, 1892, p. 318. 



Geo. P. Becker : Finite] logeneous strain, Mow ami rupture of rocks. Bull. Geol. Soc. Am., vol. 



4, 1893, pp. 13-90. 



