706 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



sands, locally reddened with Iron in the lower part, where the waters ha-s-e 

 stood on the surface of the clays. 



Over all the broad plain south of Mount Warner, over which the road 

 from Amherst to Northamj^ton runs, the passage beds, seem to me to be 

 present, and the clays seem still to retain their full height. 



EXPLANATION OF THE STRUCTURE OF THE CLAYS. 



In introduction of this explanation a further jieeuliarity of the clays 

 may be here considered. 



While the "fat" portions of the clay layers are very uniform in thick- 

 ness and grain, the variation in the thickness of the layers depends upon a 

 thickening or thinning of the sandy portions of these layers, which may or 

 may not be accompanied by a corresponding change in the grain of the 

 latter. At times the fat laminae separate and take in between them 12 to 16 

 inches of a sand but little coarser than that of the coarse jiortion of the 

 layers at the Hadley locality, as is the case in a large portion of the Wap- 

 piug cutting. At other times the grain increases to medium or coarse. 



The fat laminae seem to be purely a sediment of matter held in suspen- 

 sion when there was scarcely a trace of current, the lean laminae to contain 

 in gradually increasing proportion the fine material carried over the bottom 

 by the friction of a slow current, which was regularly intensified for the 

 formation of the thin films of sand which separate the layers. One finds 

 these clays as regular as a pile of thin deals over all the basin, and I imag- 

 ine that each layer represents a year's work of the flooded river. The fat 

 layers were thrown down in the winter impartially over every portion of the 

 lake bottom, and with the breaking up of the ice in spring the flood swept 

 it off" those portions where it had strong current, at times just crumpling 

 it, as shown in figs. 39 and 40, p. 647, but over the deep lake bottom only 

 rippling its surface, the fat tenacious clay resisting erosion slightly, while the 

 coarse material brought in by the tributaries was pushed in sheets out over 

 the delta flats and dumped over their fronts, and in small quantity earned 

 out over the clays. In exceptional floods thin films of these sands were 

 carried down across the very middle of the lake, as at the Hadley locality, 

 and came at the beginning of the spring, for the coarse sand rests directly 

 in rippled hollows of the surface of the finest clay. In this sand are found 

 the twigs and reeds and leaves broug-ht down by the tributaries, and the 



