4i6 REVIEWS 



The Potsdam sandstone is thought to represent the residuum of 

 insoluble material from deep and thorough weathering of pre-Cambrian 

 gneiss and quartzite. The total absence of fossils, the undercut erosion 

 in the Grenville quartzite at some of the contacts, the fine and even 

 nature of the sand itself right up to the contacts suggest a wind-blown 

 origin. The position, the tillite-like nature, and many other features of 

 some of the basal beds of the Potsdam suggest glacial deposits but no 

 striated pebbles were found. The late pre-Cambrian and Cambrian 

 history of this region is thought to have been as follows: (i) peneplana- 

 tion, then (2) uplift and further deep weathering under a moist and 

 warm climate, next possibly (3) glaciation followed by (4) arid, cold, 

 desert conditions, and finally (5) slow submergence and encroaching of 

 sea from the northeast. The late Cambrian and early Ordovician record 

 is one of intermittent submergence and elevation. From the history of 

 the region to the north it is almost certain that Chazy, Black River, and 

 Trenton seas covered this area but their deposits have all been removed 

 by erosion with the possible exception of a local thin bed of Trenton 

 limestone. By the end of the Mesozoic the general region had been 

 reduced to a peneplain. This peneplained surface is recorded by the 

 high land with a nearly even sky-line. This peneplain was elevated, 

 dissected by Tertiary rivers, and before Pleistocene glaciation, wide flat 

 areas were developed which record a late Tertiary peneplain. The 

 author calls attention to the close resemblance between the Mesozoic, 

 Tertiary, and recent history of the region and the late pre-Cambrian 

 and Cambrian history as outlined above. 



J. F. W. 



The Pre-Cambrian Rocks of the Canton Quadrangle. By James C. 

 Martin. New York State Museum Bulletin, No. 185. 

 Albany, N.Y., 1916. Pp. 112, pis. 20, figs. 30, maps i. 



The Canton Quadrangle lies in northwestern New York State about 

 12 miles east of Ogdensburg on the St. Lawrence River and 30 miles east 

 of the Thousand Islands region. The geology is very similar to that of 

 the Adirondack Mountains while the physiography is that of a line of 

 foothills which mark the approach of the rugged interior to the southeast. 



The oldest rocks, Grenville sediments, are crystalline limestone, 

 garnet gneiss, quartzite, quartz-schist, and various other siliceous and 

 pyritous gneisses. Owing to intense post-Grenville deformation no 

 good continuous sections of the sediments remain, but the probable 

 thickness is somewhere about two or three miles. The various rock 



