178 [Assembly 



and it is traced into New Fairfield and Danbury, Connecticut. Dr. 

 Percival did not recognize in it the same general characters as in his 

 " Gra7iitic Formations," but put it under the head of " Calciferous 

 Micaceous Formation (gneiss)" and represented it by H. 2. B. on his 

 geological map. He calls it a table-land bounded north and south 

 as indicated above. In his description of the rocks of this division 

 or formation a granitic gneiss is mentioned as predominating with 

 beds of dark liornblendic and suh-hornhUndic rocks and dark micaceous 

 rocks. And he adds that a range of the latter is traceable wesL 

 beyond the Croton, between Carmel and Somers.* An examination 

 of the outcrops on two sections across this division of Dr. Percival, 

 one from Brewster's, north-east to Valleyville and Quaker brook hol- 

 low, and the other from Brewsters through Southeast Centre and 

 Milltown and across Joe's hill, failed to show sufficiently marked and 

 distinctive rock characters to separate it from the gneisses, granulytes, 

 syenite-gneisses and micaceous schists common to the Highlands to 

 the west. 



The southern limits of the Archrean rocks of the Highlands from 

 the State line east of Brewsters to the Hudson river may be described 

 as follows : Beginning near Mill Plain, Conn., and at the southern 

 foot of the Joe's hill ridge, the line follows the east and west valley 

 to near Southeast Centre and then the Croton river, passing south-east 

 and south of Brewsters. This valley has in it a white limestone and 

 a micaceous quartzite, as also mica schist, and these sedimentary 

 rocks have a general east and west strike and a northward dip. Joe's 

 hill is the southernmost ridge of gneiss of the belt, whose boundaries 

 are here given, and the limestone and schistose rocks are the adjacent 

 bounding formations. South-west of Brewsters the tracing of the 

 geological line is rendered difficult by the absence of distinguishing 

 characteristics in the rocks which occur in the undoubted Archaean 

 belt north-west of the Croton river, and some of the outcrops of 

 gneiss which are traceable in a narrow belt eastward from north of 

 Croton falls to Peach lake and into Ridgefield and Danburv in Con- 

 necticut. The schists in the southern part of the town of Southeast 

 and north of Peach lake border this belt of gneiss on the north and 

 the Salem limestone is contiguous on the south. The prevailing 

 north-east dip makes an angle with the mean direction of that of the 

 beds in the outcrops of the Theall mine and along the Croton valley, 

 but no contact phenomena or localities of unconformable strata were 

 observed. So far as rock composition is concerned there is more mica 

 and a more schistose structure in the rocks of this Croton falls and 

 Peach lake gneissic tongue, if it be viewed as an extension eastward 

 of the Archgean. Garnet also is common in these rocks; and they 

 have a striped or banded appearance. But there is the absence of 

 well-marked distinctions which are at once recognized in the outcrops 

 on the two sides of the boundary line as traced across Putnam and in 

 Dutchess counties. 



From the Croton river west the general course of the southern line 

 of the Highlands belt is westerly, but it is marked by several loops, 

 which stretch southward around the Archaean projecting ridges, as it 



* Fercival's Report on the Geology of Connecticut, 1842, pp. 83 and 92, 93. 



