T. JV. Dale — Algonkian- Cambrian Boundary. 123 



The pebbles of the North Sherburne conglomerate are nearly 

 all quartzite and measure up to two feet in length and eight 

 inches in width. Fig. 1 shows the form of these pebbles. 

 Some of them seem to have been elongated in metamor- 

 phism. One from a loose block from the same ledge measures 

 15 x 1-6 x 2-J inches. The quartzite of these pebbles in thin 

 section shows the presence of a little muscovite, chlorite, sider- 

 ite passing into limonite, and grains of zircon. A section of 



Fig. 1. 





Fig. 1. Diagram-sketch of north side of anE.-W. joint in Algonkian con- 

 glomerate showing sections of quartzite pebbles. North Sherburne, Ver- 

 mont. 



the quartzite of the thick bed shows quartz grains much strained 

 and granulated, and a little muscovite and chlorite, and limon- 

 ite stain of uncertain source. There is thus no marked differ- 

 ence between the material of the pebbles and that of the bed. 

 The cement of the conglomerate is muscovite-quartz-chlorite 

 schist. 



Inductions. — The original general strike of the pre-Cambrian 

 granite-gneiss and the associated Algonkian sedimentaries in 

 the southern 60 miles of the Green Mountain range in Ver- 

 mont was probably about W.jS"W. and was due to the direc- 

 tion of the post- Algonkian movement. The general strike in 

 the same region of the Cambrian beds east of the pre-Cambrian 

 was about N. 30° E., and was due to the direction of the post- 

 Ordovician movement, but in many places the pre-Cambrian 

 rocks yielded to the later crustal contraction and acquired a 



Am. Jour. Sci. 

 9 



-Fourth Series, Vol. XLII, No. 248.— August, 1916. 



