FOLDS. 253 



Mountains, whoso great thickness sometimes as much as ten miles forbids the supposi- 

 tion that it could be only a single fold, and compels us to believe that the same strata 

 must have been doubled several times, and so brought into apposition, with a nearly per- 

 pendicular dip, that we cannot distinguish one fold from another. We know of no other 

 way to explain the enormous thickness of these strata, unless it be to suppose what seem 

 to be strata to be in fact only foliation or cleavage, which have been superinduced, and do 

 not correspond to original stratification. We doubt not that these structures are 

 superinduced and do sometimes intersect the planes of stratification and lamination. 

 But the not unusual occurrence of beds of quartz, and sometimes feldspathic compounds, 

 whose bounding planes are parallel to those of the schist, shows that the foliation and 

 cleavage do generally correspond to the stratification. Hence where we find enormous 

 thicknesses of homogeneous schists, whether with inverted or normal dips, the most sim- 

 ple explanation is, that they consist of a succession of folds so closely appressed that we 

 cannot tell where one ends and another begins. 



To the right of the folds, h, i, k, on the preceding diagram, we have represented stratified 

 masses mantling over an unstratified mass, though the upper part of the fold has been 

 denuded. Such cases may be found occasionally in the eastern part of Vermont, as our 

 general sections will show, say Sections III, IX, X and XII. Still more to the right we 

 give a mass of unstratified rock, m, lying as a bed between the strata; which, as already 

 stated, is the most usual mode in which such rocks occur in Vermont ; as for instance at 

 Ascutney and Greensboro, and on several of the more northern sections. 



Where several rocks are interstratified, it is frequently not difficult to determine the 

 limits of a fold, even though we have only parallel strata with the same dip, and that an 

 inverted one, as at c, on our section. For we find a similar succession of rocks in passing 

 each way from the axis of the fold. Several are represented on c, with an inverted dip, 

 and the same number on g, with a dip partially inverted. 



It is often a very difficult matter to ascertain whether a rock is inverted or in a normal 

 position. If the former, we shall find ripple marks, tracks, rain drops, and fossils, bottom 

 upwards. Yet it is not easy always to settle this point ; and many rocks have no such 

 appearances from which to judge. 



If strata have been thrown over so as to form an inverted axis, the natural inference is, 

 that the newest formations will be found at the bottom, and the oldest at the top. But 

 this is true of only one side of a fold. Thus in the fold, c, it is only the rocks on the left 

 hand side of the axis that present an inverted order; those on the right hand side are in 

 their normal position. In the synclinal fold, /, the left hand branch of the fold is in a 

 normal position, the right hand slightly inverted ; but as there is only one sort of rock, 

 we cannot point out the part that is inverted. In the fold, g, the strata on both sides of 

 the axis are in a normal position ; so in the folds, 7, i, k, the strata being perpendicular, we 

 cannot say that some layers are above or beneath the others. As a matter of fact, how- 

 ever, in Vermont the talcose schist which these folds loosely represent, generally has a 

 high southeasterly dip, which according to the reasoning above, will make the left hand 

 side of the folds in an abnormal position, and the right hand side normal. 



If these illustrations be admitted as giving an approximate idea of the position of the 

 rocks in Vermont, and of the manner in which they have been plicated and overturned, 



