1 6 NEW YORK STATE MUSEUM 



Further detailed field observations tend to confirm the opinion 

 previously given that metamorphosed sediments constitute the 

 most ancient rock types of this region and that they are the 

 equivalents of the Grenville series as known in the Adirondacks. 



Work on the Poughkecpsie quadrangle has been carried forward 

 by Prof. C. H. Gordon, who reports as follows : 



Precambric. Some portions of the gneissic areas were re- 

 viewed with care. It has seemed entirely possible to establish the 

 identity of the rocks which make up the narrow strip that ex- 

 tends from the carpet mills at Wolcottville northeastward to 

 Vly mountain with the gneisses of the Fishkill mountains. This 

 strip, which will be referred to as the Glenham belt, was de- 

 scribed by Mather as the " Matteawan granite." 



The rocks which make up its major portion vary from greenish 

 granitic types of rather massive character to more gneissoid and 

 usually somewhat finer grained rocks with reddish color. The 

 primary minerals composing these two varieties are quite simi- 

 lar and are quartz, microcline or orthoclase, plagioclase and bio- 

 tite. The last named has undergone alteration which appears 

 to be an ancient character. During the period of this alteration 

 the biotite was more or less completely changed to chlorite and 

 considerable quantities of iron oxids were liberated. Occasion- 

 ally the granitic rock passes into a type with scarcely any ferro- 

 magnesian minerals, with milky quartz and a feldspar pink from 

 disseminated iron particles. These varieties grade into one 

 another although the greenish rock is most abundant in the 

 southern end of the strip and the gneissoid type around Vly 

 mountain. The varieties just described are those which have 

 been emphasized by most observers and have been called 

 " altered sandstone,'* " bastard granite," etc. 



Within the last two or three years new cuts have been opened 

 in this strip in the process of evening up the grade on the road 

 from Fishkill village to Wappinger Falls. This road cuts the 

 strip about midway of its length. Among the rock varieties 

 exposed in these cuts are hornblende and micaceous gneisses 

 quite similar to some of those seen in the Fishkill mountains 

 and several varieties of altered gneissic derivatives. Epidote is 

 abundant in many outcrops. 



It has proved possible to trace in a satisfactory manner the 

 rocks composing this strip through somewhat similar masses 

 lying at the south in Matteawan to the base of the Fishkill moun- 

 tains. Rocks identical with the altered and epidotic gneisses 



