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NEW YORK STATE MUSEUM 



shut the lowland off on the north about the margin of the Fort 

 Edward plain is in great part dependent on the preglacial his- 

 tory of the district. Throughout this area the graptolitic rocks 

 forming the argillaceous facies of the Lower JSiluric known as 

 the Hudson river group and comprising the Lorraine and other 

 bodies of fossiliferous shale form the walls and floor of 

 the Hudson river valley and its gorge. All of the glacial erosion 

 on this terrane could not but produce clay at every step in the 

 trituration of the material. The shales even where more or less 

 mountain built and cleaved give way in small bits rather than 

 those large fragments which the ice sheet was enabled to drag 

 out from jointed sections of the harder rocks in the districts on 

 the east and west. To this original clay of the valley there was 

 added the rock-flour brought in from the higher grounds of the 

 valley sides whenever and wherever the drainage was free to 

 concentrate in the main channel. Moreover during the draining 

 of Lake Vermont (glacial Lake Champlain) much clay was moved 

 southward and left in the upper Hudson valley. 



Organisms of the clays in the Hudson river valley. A long and 

 fairly diligent search has been made for fossils in the Albany 

 clays and the earlier deposits which occur farther south in the 

 Hudson river valley but without the finding of fossils which 

 indicate the presence of the sea during the stages of clay deposi- 

 tion. 



Ries has discovered the spicules of a sponge (Hyalonema) and 

 fresh-water diatoms Navicula gruendeleri As., Xavicula permagna 

 Edw., Melosira granulata (Ehr.) Ralfs., Nitzschia granulata 

 (Gruend) . He also reports finding impressions in the blue clay at 

 Croton Landing which the late Professor Hall regarded as worm 

 tracks. 



I have collected small sinuous trails from the clays at South 

 Bethlehem agreeing closely with those mentioned by Emerson 1 

 from the clays of the Connecticut valley and referred to the 

 larva of a dipterous insect (Chwmomos motilator). 



J. Eights in 1852 described fossil leaves from the clays near 

 Albany. Emerson 2 mentions leaves known as Mitchella repens 



1 Emerson, B. K. Geology of Old Hamden and Hampshire Counties, 

 Mass. U. S. Geol. Snr. Monogr. 43, p.T20. 



2 7. c. p.718. 



