Association of American Geologists and Naturalists. 153 



the most ancient depository of organic life hitherto discovered in our stra- 

 ta. Adjoining this great mass of arenaceous strata towards the southeast, 

 we find throughout much of the broad belt of the Blue Ridge, especial- 

 ly in its prolongation southwestward from the Potomac, a wide expan- 

 sion of metamorphic strata intersected by innumerable veins and dykes 

 of greenstone and other igneous materials, and displaying almost every 

 grade and variety of alteration in texture and mineral contents. These 

 after long and careful observation, we have been led to consider as a 

 group of sedimentary beds still older than the preceding ; but form- 

 ing a part of one and the same unbroken series. Thus then in the great 

 group of strata, at the base of our lowest fossiliferous series we are pre- 

 sented with similar and perhaps more striking results of igneous mod- 

 ifying powers than even in that portion of the Champlain system whose 

 metamorphosed beds constitute the Taconic group. Although no relics 

 of either vegetable or animal life have hitherto been met with in this 

 group, we cannot confidently infer their entire absence, since from the 

 effects of cleavage and chemical change their remains could not fail to 

 be greatly obscured and for the most part quite obliterated. It is most 

 probable, however, that the same barrenness of fossils remarked in the 

 slates and sandstones immediately beneath the Potsdam sandstone, pre- 

 vails throughout the whole of the continuous series of subjacent strata. 



Respecting the phenomena presented in the long belt of rocks here 

 referred to, the question suggests itself whether the so called Taconic 

 system, instead of belonging exclusively to the Champlain division, may 

 not along the western border of Vermont and Massachusetts, include 

 also some of the sandy and slaty strata here spoken of as lying beneath 

 the Potsdam sandstone. 



Applying for the present the term palaeozoic only to the strata com- 

 mencing in the ascending order with the conglomerates at the base of 

 the group, including the Potsdam sandstone, since below this there is 

 little probability of our finding traces of organic beings, the next inqui- 

 ry of general interest relates to the natural divisions, groups and forma- 

 tions, into which we should arrange the whole enormous body of sed- 

 imentary deposits, between this horizon and the top of the Coal rocks. 

 Throughout this great mass of strata, whose aggregate thickness ex- 

 ceeds in some districts thirty thousand feet, made up of an extraordinary 

 number of distinct formations, characterized by peculiar organic remains 

 and composition, and marking a long series of events and a vast lapse 

 of time, we behold one uninterrupted succession of deposits, closely 

 linked by an equally unbroken sequence of animal and vegetable remains. 



Vol. xLvii, No. 1.— April- June, 1844. 20 



