QUATERNARY DEPOSITS. 



74 



215 



Shows a series of the same large arching and folds, and angular movements. 



The above wood-cuts were copied from the drawings of Mr. Amsden, formerly an assistant 

 engineer of the Black River canal, who kindly offered his services to give a transcript in 

 miniature of the forms assumed by those disturbed layers. The engravings show three dis- 

 tinct parts : First, in the descending order, the sand which covers the clay deposit ; under 

 which is a range of undisturbed layers or thin beds of clay, resting upon the series of dis- 

 turbed ones, the object for which the engravings are given ; these in their turn, being placed 

 upon a second range of undisturbed beds, which form the bottom of the feeder. The disturb- 

 ed beds or layers are placed between two perfectly undisturbed ranges ; showing the various 

 forms of curvature, contortion, plication, wrinkles or folded axes, by which such appearances 

 have been named. These disturbances extend for a considerable distance along the feeder, 

 though of but little thickness. The beds both below and above the contorted ones, are per- 

 fectly imdisturbed throughout their whole course, as represented in the engravings ; but the 

 disturbed layers do not possess this uniformity, for they exhibit portions that are undisturbed. 

 When the disturbed portions are compared with the undisturbed ones of the same layer, they 

 show that the former were raised, greater space being required by the layer where contorted 

 than where undisturbed. These interesting forms of disturbance were no doubt the result of 

 unequal, local and lateral pressure, which the nature of the country admits ; for such forces 

 must have operated when the immense mass of alluvial which once covered all that part of 

 the valley where the Black river now flows, was swept away. 



