148 C. L. WHITTLE METAM0EPH10 CONGLOMERATE. 



Metamorphic Conglomerate. 



Approximate Relation to known, geologic Horizon. — The geologic position 

 of the limestone and quartzite of the Rutland valley has lately been de- 

 termined definitely,' 1 ' the limestone paleontologieally and the quartzite 

 stratigraphically. 



Occurring next below the limestone, the quartzite is the northern 

 continuation of the Clarksburg-mountain quartzite, in Massachusetts, 

 in which Walcott has found the Olenellus fauna characteristic of the 

 Lower Cambrian horizon. About one mile north of Rutland village, in 

 Vermont, Dr Wolf and Dr Foerste were fortunate enough to find Lower 

 Cambrian fossils in a silicious limestone that lies superjacent to the 

 quartzite. Northeast of Rutland the quartzite is found associated with a 

 sandy phyllitic schist that belongs to a series of metamorphosed elastics 

 having a vitreous quartzite or conglomerate at its base. This whole 

 series, barring the Lower Cambrian quartzite and limestone, has been 

 subjected to the most intense dynamic action. The sequence of the dif- 

 ferent members of the series is in many regions hopelessly obliterated 

 and confused by the mountain-building forces that have produced new 

 structural planes, a new mineralogic composition, and have additionally 

 complicated the geologic order of succession by sharp folding, which is, 

 as a rule, too much involved for decipherment. These phenomena are 

 particularly noticeable in the conglomerate horizon and its many phases, 

 and it is in this rock that I wish to describe some of the evidences and 

 effects of metamorphism shown by the destruction of old clastic minerals 

 and in the production of new ones. 



OTTRELITE SCHIST. 



Occurrence and Extent. — One of the most conspicuous phases of the con- 

 glomerate is due to the development of ottrelite in great abundance, so 

 that it is not uncommon to find fully 25 per cent of the rock made up of 

 this mineral. The ottrelite is commonly most abundantly developed 

 where the rock has now a well-marked schistose character that is either 

 due to an original finer-grained deposit or is a result of the shearing and 

 crushing action of dynamic forces. It is often found, however, occurring 

 in the grouudmass of the coarsest conglomerate or along planes of shear- 

 ing in a blue, hyaline quartzite. Still another phase is more nearly mas- 

 sive, fully 40 per cent being ottrelite, the rock at first sight simulating 

 in appearance some porphyritic hornblende dike. The rock is a very 



*"0n the Lower Cambrian Age "t the Stoekbridge Limestone" : Bull. Geol. Soe. Am., vol. •_. 1880 

 pp. 331-338. 



