40 NEW YORK STATE MUSEUM 



listed^^ eleven areas (outliers) of strata of Upper Cambrian (Pots- 

 dam to Little Falls) age well within the southeastern Adirondack 

 Precambrian rock area. The two outliers discovered in the Luzerne 

 quadrangle in 1920 bring the total known outliers up to thirteen. 

 The outliers containing marine Upper Cambrian strata at Wells, 

 Hamilton county; in Essex county, near Nlorth River; at and near 

 Schroon Lake village, Essex county; and in the northern part of 

 the Luzerne quadrangle are of great geological significance because 

 they are separated by many miles from the large areas of rocks of 

 the same age south and east of the Adirondacks and, therefore, 

 prove that the late Cambrian sea spread over the southeastern Adi- 

 rondacks, including the area of the Luzerne quadrangle. 



Based upon the presence of Middle Ordovician strata with fossils 

 in the outlier at Wells, and the nature of the overlap of the Ordo- 

 vician upon the Precambrian of the southern and eastern Adiron- 

 dacks, the writer some years ago showed^^ that the Middle Ordovi- 

 cian sea must have extended even farther than the late Cambrian 

 sea from the southeast toward the central Adirondack area. Studies 

 on the southern side of the Adirondacks have shown that the Upper 

 Cambrian and Ordovician strata are separated by an unconformity. 

 Accordingl}'', the late Cambrian sea spread over the area of the 

 Luzerne quadrangle and was excluded toward the close of the 

 period by emergence of the land which underwent some erosion. 

 Then, during the first half of the Ordovician period, the sea again 

 spread over the area of the quadrangle. There is no evidence what- 

 ever that any sea later than the Ordovician ever covered the south- 

 eastern Adirondacks. It is possible, however, that somewhat later 

 marine waters did transgress upon the region, and that the result- 

 ing deposits have since been completely removed by erosion. 



STRUCTURAL GEOLOGY 

 Structure of the Grenville Series 



Evidence has recently been presented ^* by the writer to show 

 that the Grenville strata of the Adirondacks have never been highly 

 folded or severely compressed. Many broad belts of the strata are 

 known to be practically horizontal or only very moderately folded, 

 as, for example, in the North Creek quadrangle, while many masses 

 are merely tilted or domed at various angles. Very locally the 



' N. Y. State Mus. Bui. 213, 1919, p. 68. 

 ' N. Y. State Mus. Bui. 164, 1913, P- 80-94. 

 'Jour. Geol., 24, 1916, p. 588-96. 



