52 CLASSIFICATION OF HOCKS. 



According to these views an important practical question in respect to metamorphism 

 is, what was the original rock from which the metamorphosed deposit was derived ? In 

 respect to the rocks of Vermont all other points are easy, compared with this. We shall 

 do all we can to make out the identification, but, in not a few instances so complete has 

 been the metamorphism, and so greatly have the strata been disturbed, that on the one 

 hand we lose the clue with the newer and known rocks, and on the other cannot tell 

 whether the rock we are examining may not belong to the oldest of the crystalline rocks, 

 the date of whose metamorphism seems to have been earlier than the Silurian or perhaps 

 even the Cambrian period. The facts we have detailed above, do indeed throw very 

 much light on the process of metamorphism ; but we feel by no means confident as to 

 the age of the conglomerate which has furnished the data ; and hence we are left in doubt 

 as to the age of the associated rocks. We have other evidence, however, which makes it 

 probable that most of the highly metamorphosed rocks of Vermont are altered Devonian 

 and Silurian formations. In the western part of the State, and especially in that part 

 of New York that lies southwesterly, we find these fossiliferous rocks but little altered, 

 and these form a good starting point for the Green Mountain rocks and those farther east. 



We regret that we have been obliged to make these preliminaries so technical, and to 

 presume upon no little knowledge of geology in the reader. But no language less 

 technical could explain the subject, and no one unacquainted with the leading principles 

 of metamorphism can understand the rocks of Vermont. The course we have taken, 

 therefore, seemed to be a kind of necessity. We now proceed to give a detailed descrip- 

 tion of the rocks of the State in such an order as we judge upon the whole to be best. 



CLASSIFICATION OF BOCKS. 



It may be desirable, before we proceed, to give an outline of the classification or order 

 which geologists have adopted for the rocks. This has become, in consequence of the 

 discoveries in respect to metamorphism, a matter of no small difficulty. The great out- 

 lines are indeed clear and satisfactory. To divide rocks into the stratified and unstratitied, 

 and then the stratified class into the fossiliferous and unfossiliferous, is natural, and is merely 

 the expression of certain facts. But when we subdivide the stratified class further, it is 

 very difficult to avoid terms that are based on theories that may be true or may not. This 

 was the objection to the old division into Primary, Transition, Secondary, &c., and in conse- 

 quence of this chiefly, they have nearly passed into desuetude. Some of the terms that 

 have been proposed as substitutes seem to us not much better. Prof. Scdgwick proposed 

 the name Hypozoic for such crystalline unfossiliferous rocks as lie below the fossiliferous. 

 But in Vermont and other parts of the world some rocks of this kind lie above the fossil- 

 iferous. Azoic that is, destitute of fossils is not liable to these objections and is a far 

 better term. The older slates and schists without fossils have been described by Sir 

 Charles Lyell as metamorphic or stratified crystalline rocks. But why call these meta- 

 morphic when the term applies quite as well to a multitude of other rocks stratified and 

 unstratified ? Often, too, these are less crystalline than formations that lie above them. 

 Sir Charles also designates these rocks along with the unstratified that are crystalline as 

 J/>/j>offene or nether- formed, and he says that " they never repose on strata containing organic 



