THE EASTERN AREA. 395 



peculiar rooks are of great interest because they sIioxa- liow closel}- u 

 eoiiii)letely crystalline and a fra<i'niental rock maA' resemble eacli other. 

 Tlie resemblance in the ledge is at times so close as to make it iiin)()ssil)h- to 

 determine where tlie massive granite ends and tlie {'ra<.;-mcnta] rock beL;ins. 



The- conglomerates differ from the recomposed granites in that among 

 the fragments of which they are contained are other materials witli the 

 granite delwis. They are generall}- closely associated with the recomposed 

 granites, ])oth often occurring within a short distance of each other and 

 practically in the same exposure. As would natin-ally be expected, simple 

 and complex granite fragments are very abundant in the associated con- 

 glomerates, but mingled -with these granite fragments are white (piartz, 

 green schist, and less frequently other varieties of pebbles. The matrix 

 of the conglomerates is essentially like that of the reconlposed granites. 

 In general the matrix is more al)undant, tlie simple grains of quartz Itni'iecl 

 in the matrices are often enlarged, and in a few cases the feldspar fragments 

 also appear to have undergone a second growth. 



Closely associated with the reconq^osed granites and the conglomerates 

 are cherty quartzites and chert-breccias. The chert-breccias are a variety 

 of rock in which a background of almost pure chert detritus contains 

 rounded and angular fragments of the same material. In its purest pliase 

 finely crystalline and amorphous silica ouly is present. In the clierty 

 quartzites a background of chert and ferriferous carbonate contains much 

 fragmental material. By short steps the chert-breccias and chei"t)' tjuart- 

 zites grade into each other. 



The close association of the recomposed granites, the conglomerates, 

 and the chert-breccias and quartzites coiTCsponds to their lithological 

 character, their matrices being essentially the same in each case. In the 

 carbonated cherts nonfragmental sedimentation has prevailed almost to the 

 exclusion of mechanical sedimentation. In the ferro-dolomitic and (•herty 

 (juartzites, while nonfragmental sedimentation was going- on, a large anioimt 

 of fraOTTiental material was Ijrcmg'ht in and intermingled. In the con- 

 glomerates and recomposed granites mechanical sedimentation was prepon- 

 derant, ])ut a sufficient amount of a nonfragmental sedimentation occurred 

 simultaneously to finnly cement the tiastic material. 



