94 NEW YORK STATE MUSEUM 



areal spread in this region and its nearest ledges are on the north- 

 western corner of Crown point. The direction thus indicated falls 

 in line with the scratches mentioned under the next topic but one, 

 and is directly opposed to an outward and expiring movement of 

 local glaciation to the northeast. The road which formerly existed 

 parallel to Grove brook has been destroyed by a freshet. 



Glacial boulders. Boulders of moderate size which have been 

 brought in by the ice sheet are of almost universal distribution. 

 They, however, are of special interest only when thty are of some 

 rock of sharply defined character and one contrasted with the 

 ledges on which it may rest. The most striking of the boulders 

 consist of Potsdam quartzite, an exceedingly hard rock, of a pale 

 yellowish color. Even on the mountain tops these boulders appear, 

 having undoubtedly been derived from the Paleozoic lowlands to 

 the northeast. The remaining Paleozoic formations are rarely seen, 

 but in this and 'adjacent quadrangles all have been noted except 

 Utica slate. 



Anorthosite is a rock which is tough especially when crushed and 

 recemented, and which lends itself readily to transportation. It 

 is significant when found amid areas of contrasted formations. It 

 is one of the most frequent boulders wherever there are anorthosite 

 areas to the northeast. The syenitic and granitic gneisses are also 

 common. A very few boulders of the crystalline limestone of the 

 Grenville series and of the associated hornblendic schists have been 

 observed but they are uncommon because of their poor resisting 

 qualities and because of the relatively small areal distribution of 

 the parent ledges. 



A mile north of Port Henry and near the rose-quartz locality 

 one small boulder of pink trachyte (or bostonite) was found. This 

 rock occurs in several dikes in the Paleozoic strata at Essex and 

 along the Vermont shore, especially on Shelburne point, but beyond 

 a probable derivation from the northeast, its source can not be 

 more sharply located. 



As to the size of boulders the general range is from half a foot 

 to 2 or 3 feet. Plate 12 illustrates one of fairly good size on the 

 southern slope of Barton hill just below the ore bed. It is some- 

 what pear-shaped and is about 10 feet in diameter. The largest 

 boulder noted, is in the woods, northwest of the Grenville area on 

 Stacy brook. As paced off, it was 20 feet by 15 feet by 12 feet. 



Glacial scratches. The scorings of the continental glacier which 

 have been preserved are almost exclusively in the valleys and are 

 best shown upon those surfaces of Beekmantown limestone which 



