INFERENCES. 257 



some of its lowest places, as at Mount Holly, where at least 8,000 feet of strata have been 

 denuded, it is possible that some of the oldest rocks may be here brought into view. 

 Hence we think it a hasty conclusion to infer positively that none of the rocks in Vermont, 

 and probably not in New England, are older than the silurian. It may be so, but it re- 

 remains to be proved. Long and patient research will be requisite to prove the true age 

 of all our metamorphic foliated rocks. 



In these preliminary remarks we have been obliged to presume upon some knowledge 

 at least, of all the rocks yet to be described. For the relations of these rocks could not 

 be well understood without these preliminary principles. Any one who chooses, after he 

 has read the detailed description of the rocks, can revert to these principles, and he will 

 understand them better. Having given this expose', the Principal of the survey will now 

 introduce the detailed descriptions, all of which in Part II. have been prepared by C. H. 

 Hitchcock, because he has had an opportunity to study them in the field more 

 thoroughly than it has been possible for the Principal to do. 



The following is a list of the rocks occurring in Vermont, and embraced in Part II, 

 reckoned in an ascending order ; though in regard to the position of those above the 

 Hudson River Group, we have little but conjecture to guide us : 



LAURENTIAN OK HYPOZOIC GNEISS. HUDSON RIVER GROUP. 



POTSDAM SANDSTONE. RED SANDSTONE SERIES. 



CALCIFEROUS SANDROCK. QUARTZ ROCK. 



CHAZY LIMESTONE. GEORGIA GROUP. 



BIRDSEYE LIMESTONE. TALCOSE CONGLOMERATE. 



BLACK RIVER LIMESTONE. EOLIAN LIMESTONE. 



TRENTON LIMESTONE. TALCOID SCHISTS. 



UTICA SLATE. UPPER HELDERBERG LIMESTONE. 



These rocks embrace nearly all the fossils found in the State, excepting those of the 

 tertiary and alluvial. The descriptions of the fossils have been taken from the highest 

 paloeontological authorities, especially from Prof. James Hall, of Albany. To him, as 

 stated elsewhere, we have been indebted for giving names to the specimens and describing 

 the few new species which we have found. 



LAUEENTIAN SYSTEM. 



The oldest rocks upon the globe, or the bottom rocks, have been denominated by Sir 

 W. E. Logan the Laurentian System, because they are well developed in the Laurentine 

 Mountains in Canada. This is the best local name for rocks of this age that has ever 

 been proposed in this country ; and we therefore use it to distinguish a particular belt of 

 rock in Vermont. This appellation distinguishes the ante-Cambrian crystalline rocks 

 from the metamorphic strata occupying most of the area of Vermont, as well as of New 

 England. It has been supposed by most geologists (and the view is still held by 

 some), that all the azoic rocks of New England are of the same age with those in north- 

 ern New York and Canada, i. e., hypozoic. But considerations will be presented in this 

 Report to show that probably most of the azoic rocks of Vermont are more recent than 

 the Laurentian ; and that consequently the separation of the azoic rocks into the Lauren- 



