HORNBLENDE SCHIST. 471 



as we might expect this back bone of the State would be. It would at least be as old as 

 the Hudson River group. But on this subject the clue by which we are trying to feel 

 our way is faint and feeble. We think, however, that a little light has broken in upon 

 this darkness, and we have a hope that the problem will one day be satisfactorily solved. 



HORNBLENDE SCHIST. 



BT C. H. H. 



Hornblende predominates in this rock, but its varieties contain feldspar, quartz and 

 mica. When it is pure hornblende its stratification is often indistinct. It does not form 

 a large group or formation by itself, but is generally interstratificd with other rocks, as 

 clay slate, mica schist and gneiss. We shall not attempt to describe all the hornblende 

 schist in the State, but simply half a dozen bands of it, which are sufficiently extensive to 

 have a place upon the map. 



Lithological Characters. 



There are four varieties of hornblende schist in Vermont. They are 



1. Hornblende alone. 



2. Hornblende and feldspar. 



3. Hornblende and quartz. 



4. Hornblende, feldspar and quartz. 



I. HOENBLENDE ALONE. 



This is the rock often denominated hornblende rock, in this Keport. It is one of the most common of 

 all the varieties, and is by no means confined to the several bands of hornblende schist represented upon 

 the map. It is found associated with gneiss and clay slate, in positions much like dikes, as well as in 

 regular beds. Its structure may be highly crystalline, or nearly homogeneous. In the latter case, the rock 

 appears to be entirely destitute of stratification or foliation. In the former case, it may form thick folia, 

 or very narrow beds, separated by planes much like cleavage planes. This variety reminds one much of 

 clay slate. For a good example of it, we refer to the hill west of the Methodist church, in Marlboro, in 

 the west part of the town. 



II. HORNBLENDE AND FELDSPAE. 



Generally the hornblende is crystalline, and the feldspar foliated, or granular ; but sometimes both ingre- 

 dients are compact. There is rarely any distinct marks of this rock, except that the whole deposit is in 

 the form of a bed. When the crystals of feldspar are large, and are rather numerous, the rock resembles 

 porphyry, although the strict definition of porphyry that the basis rock and the crystals should be com- 

 posed of the same mineral does not apply to it. But we have in various places spoken of this rock as 

 porphyritic hornblende, because the rock so closely resembles true porphyry. The best development of it 

 in the State, is at Williamsville. It occupies an area there of nearly a square mile, lying between the 

 gneiss and calciferous mica schist. Crystals of rutile and ilmenite are found in it, associated with chlorite. 

 Bowlders from this locality are found scattered all over the Connecticut River valley, in Massachusetts. 

 Another bed of this rock is in the east part of the calciferous mica schist in Norwich. A similar rock of 

 great width is described under talcose schist in Waterford. 



III. HOENBLENDE AND QUARTZ. 



True hornblende schist is properly a foliated mixture of hornblende and quartz. The hornblende in 

 crystals forms the principal ingredient, however. The quartz is granular. This passes insensibly into the 

 next variety. The rock is slaty ; and is sometimes traversed by veins of quartz or granite. 



