GLACIAL AND POST-GLACIAL HISTORY 419 



The Hudson Valley has three natural divisions: (i) the part south 

 of the Highlands from Peekskill to the narrows at Brooklyn; (2) the 

 Highlands from Peekskill north to near Fishkill; and (3) the broader 

 Hudson Valley from near Fishkill to north of Glens Falls. 



North of the Hudson Valley is the Champlain Valley, to which two 

 passages lead, one by way of Lake George and the other east of 

 the Lake George pass by way of southern Lake Champlain. The 

 broader Hudson Valley and the Champlain Valley have been con- 

 sidered the northeastward continuation of the Greater Appalachian 

 Valley. 



SUB-LACUSTRINE OR SUB-MARINE GLACIAL DEPOSITS IN THE 

 HUDSON AND CHAMPLAIN VALLEYS. 



In the bottom of the Hudson and Champlain Valleys there has been 

 built in recent geological times a plain mainly of clay, with margins 

 frequently of gravel and sand.' This plain has the form of an old 

 lake-floor or old sea-floor. The clay plain is best seen in the north- 

 ern part of the Hudson from Catskill north. In the southern part of 

 the valley — from Poughkeepsie south — it is either absent entirely, or 

 is to be seen only in limited areas, and generally covered with gravel 

 and sand. The clay in both the Hudson and Champlain Valleys is 

 laminated, with alternate "fatty" and sandy laminae having a thick- 

 ness of one-fifteenth of an inch or more. (See Fig. 2.) The laminae 

 are sometimes grouped into beds a few inches in thickness, sepa- 

 rated by rather prominent lines of parting. In one place ripple 

 marks were seen. (See Fig. 3.) The clay often shows faulting and 

 frequently shows joint structure conspicuously. (See Fig. 2.) It is 

 sometimes contorted. The upper part of the clay is generally yellow in 

 the Hudson Valley and brownish-red in the Champlain Valley. The 



I The clays and gravels and sands of the Hudson Valley have been described in 

 considerable detail by F. J. H. Merrill and Heinrich Ries in the TeniJi Annual 

 Report of the New York State Geologist, and by Mr. Ries in the Bulletin of the New 

 York State Museum, Vol. Ill, No. 12. The former report was in hand in the field, 

 and while the interpretation placed on these deposits is quite different, the \vriter wishes 

 here to make general acknowledgment of its aid in his studies. Specific acknowledg- 

 ment is made in the proper place where this report has been drawn upon for facts 

 beyond the writer's personal observation. The writer also had the aid in the field of 

 the article by S. Prentiss Baldwin on " The Pleistocene History of the Champlain 

 Valley," American Geologist, Vol. XIII (1894), pp. 170-184. 



