GEOLOGY OF MOUNT MARCY 



35 



but the feldspar is more abundant and the explanation of small angu- 

 lar fragments in a great anorthosite mass is difficult. The inclusion 

 and others in the vicinity are undoubtedly fragments of Grenville 

 sediments which have been saturated with anorthosite magma. 



A very peculiar exposure appears on Roaring brook, along the 

 trail up Giant from the Keene valley. The area is very near the 

 border of the Elizabethtown quadrangle and may be in the latter. 

 It has been mapped on the Elizabethtown sheet as a small syenite 

 area in the anorthosite. Anorthosite is the most extensively exposed 

 country rock. In the valley of the brook it shows extraordinary 

 brecciated contacts with the darker rock, which was earlier inter- 

 preted as a basic syenite but which, despite mineralogical' parallels 

 with the syenites, is now believed to be Grenville. The accompany- 

 ing figure (figure 5), is a sketch to scale of the dark inclusions, and 

 the succeeding figure (figure 6), is of a fragment of gneissoid rock, 

 whose minutest crenulations were parallel with the contact. 





■ - -I, 



< I FOOT 



Fig. 6 Detail of an incltision of Grenville gneiss in anorthosite, Roaring 



brook, Giant trail 



In Bulletin 138 (page 39) mention is made of a peculiar dark 

 rock which appears near the woolen mill, about a mile west of the 

 large hotels of Elizabethtown on the main road to the Keene valley. 

 In the bed of the brook which furnished the mill with power were 

 formerly exhibited excellent contacts against the anorthosite. The 

 relations are illustrated in detail in figure 7 of Bulletin 138. A recent 

 freshet has now buried them in sand. The rock was a dark, gneis- 

 soid variety of moderate coarseness of grain. While showing some 

 blue labradorite phenocrysts, it chiefly consisted of deep green 



