THE CAMBRIAN ROCKS OF NEW YORK, VERMONT, 

 AND QUEBEC 



By CHARLES E. RESSER 

 Curator, Division of Invertebrate Paleontology, U. S. National Museum 



Cambrian rocks were studied during the past field season in New 

 York, Vermont, and Quebec, and the work was doubly interesting 

 because it was done in very attractive portions of America. On the 

 way to the first objective in the Adirondack Mountains, Cambrian 

 outcrops in central Pennsylvania were briefly studied. Folds and 

 faults here bring up old rocks, exposing a sequence which matches 

 that of the southern Appalachians and which constitutes the most 

 northerly outcrops of the older Paleozoic beds west of the 

 Appalachian Valley. 



The first objective of the season was examination of the Potsdam 

 and related Cambrian formations on the flanks of the Adirondack 

 Mountains. During Upper Cambrian times marine waters entering 

 the continent surrounded an old rock mass, now the Adirondacks. 

 These present uplands were then evidently low islands in the Cambrian 

 sea. Today the Cambrian formations flank the mountains on the 

 northern and eastern sides but are absent by overlap of younger 

 strata on the south and west. However, the outcrops do not form a 

 continuous belt around the mountains as they must have when de- 

 posited. Inliers show that formerly the Cambrian beds extended 

 much farther in toward the center of the mountain mass than they 

 do now. Radial faults, possibly formed during the building of the 

 Appalachian Mountains to the east, separated the margins of the 

 Adirondacks into blocks, which were moved up or down with respect 

 to each other. The down-dropped blocks were protected from the 

 full force of erosion agents, particularly recent glaciation, and hence 

 retain the layers of Cambrian rocks. At many places glacial drift 

 covers large areas. Through removal of the Cambrian beds in some 

 areas and covering by glacial drift in others, only isolated patches of 

 the rocks remain for study. 



Fossils are rare in the sandstones which comprise much of the Cam- 

 brian sequence and which rest on the granitic foundation of the Adi- 

 rondacks. These sandstones grade upward into calcareous beds. Since 

 the calcareous material is chiefly magnesium, the rocks are dolomite, 

 a type of matrix which seldom preserves fossils. 



After the melting of the ice sheets, the streams radiating from the 

 higher portions of the Adirondacks flowed in new channels. Those 



