THE EASTEHN AREA. 375 



apart from the oonglomerato oiios. These slates are more freqnenth' fonnd 

 in the southern than in the nortliern part of the Ix'lt. Tlic color of the 

 rocks, whether fine gi'ained or conglomeratic, is some shade of Liiecu or 

 grayish-green. Sometimes the rocks show a schistose structure, although 

 in general tlle^' are (piite massive. The conglomeratic phases are tlie pre- 

 dominant ones, and here the fragments are very ahuudant, so as to leave 

 but little room for a matrix. Nearly all of the ])el)l)les and l)o\vlders are 

 of a single variety, pale greenish-gray, aphanitic, and massive. In some 

 localities a])hanitic, dark reddish-brown, telsitic-looking pebldes are <pnte 

 numerous, although they never become the pre(h)minant variety, ^'^ery 

 rarely worn white quartz pebbles are found. The pebldes are usually more 

 resistant theiv the matrix, and consequently protrude upon the weathered sur- 

 face in nodular or mannnillar\- forms. In the greater number of the expo- 

 sures fractni-e takes place through matrix and ])ebble with about equal ease. 

 In those exposures in wliicli the matrices are nuu-li altered, and therefore 

 schistose, fracture occurs around the pebbles to a greater or less extent, 

 depending upon the degree of alteration. The lines of separation lietween 

 the pebbles and matrices in the fresher rocks are quite sharp, but in those 

 which are more altered they are vague; and as tliere is often l)ut a slight 

 difierence in the coloi- and texture of the pebldes and matrices, when the 

 rocks are mnch altered it is ditficult to separate one from the other on a 

 fractured surface, although tlie ditl'erence is clearly seen upon the weatliered 

 surface. 



A stud\' of some fift\ tliin sections shows that tlie matrices are of many 

 phases, which vary into each other by impercepti))le gradations. At times 

 the matrix appears to l)e a fine gi-ained enq)tive, which contains fraguu-nts 

 of essentially the same material. This phase of matrix is descril)ed under 

 the greenstones of the eastern area and the descri])tion will not l)e here 

 repeated. An important fragmental kind is composed of tlie line debris 

 from material like the contained jielildes, combined witli linely crystalline 

 quartz; that is, it is a reconqxtsed green.stone, and is oiten .schisto.se. 

 The minerals most frequently found in this phase of mati-ix are (piartz, tabu- 

 lar plagioclases, clilorite, epidote, titanite ami leucoxeiu', actinolite, and, as 

 accessories, oxide of iron, a carbonate, aud occasiouall}' remnants of augite. 



