GEOLOGY OF THE CONNECTICUT VALLEY DISTRICT, 453 



hornblende and Bethlehem gneiss are well understood, the innermost be- 

 ing the oldest, it follows that the quartzite is newer than the hornblende 

 schist. It may be there is more than one quartzite in this field ; but 

 none of the authors who have written about these rocks have assumed 

 the existence of quartzite of more than one age. 



4. There was probably a long interval between the period of the depo- 

 sition of the hornblende and quartzite, so that there is an unconformity 

 between them ; and the presumption is, that the quartzite west of the 

 hornblende in Vernon lies upon the latter, both strata dipping easterly, 

 and the former may not be inverted. The possibility of inversion here 

 has been suggested heretofore. The clay slates of West mountain and 

 Guilford are universally admitted to underlie the quartzite unconform- 

 ably. Therefore we have both the period corresponding to the strati- 

 graphical break, and the time occupied by the deposition of the clay 

 slates, to represent the interval between the quartzite and hornblende 

 schist. The quartzite has also been mentioned as unconformably over 

 the hornblende east of Otter pond in Gill. The superiority of the quartz- 

 ite to the gneiss, in the absence of the hornblende, is well shown on the 

 Perchog river in Winchester (Fig. 71). 



5. It is well agreed, also, that the Coos slates overlie the quartzite. 

 This appears from the section at Mr. Williams's (Fig. 73); from the rela- 

 tions of the quartzite east of Fall river to it (Fig. 72); and from many 

 sections that have been described in the other Connecticut areas. Mr. 

 Huntington has come to the same conclusion in his essay upon the rocks 

 between Charlestown and Chesterfield. 



From these conclusions, others of importance follow. 



6. The Coos slates, starting from the Bernardston plain, cross trans- 

 versely the clay slate, quartzite, hornblende schist, and Bethlehem gneiss 

 before reaching the Chesterfield deposits of the same age, which extend 

 uninterruptedly thence to Haverhill, embracing the typical area of this 

 name in Hanover, Lyme, and Orford. Hence it is the newest of all the 

 several series named. 



7. It follows that there are important inversions in this whole field, 

 where no one would suspect their existence without a previous knowl- 

 edge of the facts now set forth. Perhaps the most singular is that of the 

 Coos slates between Fall river and South Vernon. They dip at a very 



