Origin of Valleys. 



131 



Valleys, 



Accurately to classify valleys, and assign probable causes for their 

 origin, is one of the most difficult problems in geology. The man 

 who takes only a hasty glance at the subject, is very apt to impute 

 all valleys to the action of existing streams. But it needs only a 

 slight examination to satisfy the observer that such a cause is totally 

 inadequate to the effect. It will not, for example, explain the very 

 common occurrence of one valley crossing another. Hence geolo- 

 gists have been obliged to resort to several causes to explain all the 

 phenomena. The origin of one class of vallies, they refer to the 

 original elevation and fracture of the rocks by a force acting from 

 within the earth. A second class they regard as the result of dilu- 

 vial action at various periods. A third class they suppose to result 

 from the agency of existing streams. 



I am not aware that any attempt has yet been made to classify and 

 point out the origin of the valleys of this country. Nor shall I at- 

 tempt to do this in respect to all the valleys even in Massachusetts. 

 I have no expectation of doing any thing like justice to so difficult a 

 subject, except where long local residence has afforded ample oppor- 

 tunity for re-examination and reflection. I shall therefore confine my- 

 self chiefly to the valleys in the region of Connecticut river ; though 

 if I do not greatly mistake, these are by far the most remarkable and 

 interesting in the State. 



It is only those valleys which are the result of alluvial action that 

 can be properly considered in this place. But as it will be more con- 

 venient to treat of the whole subject together, I shall here offer all 

 the remarks I have to make upon it. 



It is now generally admitted by geologists, that all stratified rocks 

 must have been originally deposited in nearly horizontal layers, and 

 subsequently elevated to their present inclined position by a force act- 

 ing beneath. Such a disturbance must have produced many violent 

 and extensive fractures in the strata and valleys of every shape. And 

 since in the mountainous parts of Massachusetts, the strata are mostly 

 primary and highly inclined, probably this is the manner in which 

 most of our mountain valleys have been produced. If, as is now 

 also generally admitted, the strata were elevated from the bottom of 

 the ocean, the retiring waters must have acted powerfully upon the 

 irregular surface, and considerably modified the forms of the valleys. 

 The agency of rains, snows, and rivers, since that period, must have 



