704 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



lower part 0.3™"", measurements of grains from the top of the layer gave 

 0.0018 to 0.00735""", from the middle of the lower portion 0.00735 to 

 0.0294""", and from the bottom 0.0735 to 0.147"°". 



At the Hatfield locality (PI. XVI, p. 690) in each layer the lower two- 

 thirds is much coarser than the upper third, and is in reality an exceedingly 

 fine sand, under the microscope appearing like a quartz sandstone, the 

 grains angular, 0.0037 to 0.0075""° in diameter. Besides quartz, there occur 

 feldspar, mica, and a few acicular microlites. The lower jjortion was olive 

 green when wet, drab wdien dry. The upper portion showed, both wet 

 and dry, a darker shade of the same color, but the ditference was much 

 more marked when it was wet. Under the microscope it appeared like 

 the other portion, except that it was much finer ; but there were present 

 many minute opaque particles of koalin, oblong or sausage-shaped, which 

 showed the Brownian movement finely. The size of the quartz grains 

 was 0.0011 to 0.002°'°". 



THE SURFACE OF THE LAYERS. 



In some cases the layers are joined so closely that one can hardly dis- 

 tinguish the line separating two laminse from that dividing the finer and 

 coarser portions of a single one. Generally there is at least a thin film of 

 rust, showing that the waters have sought out the planes of separation 

 between the layers, as affording them easier passage, and the clays on dry- 

 ing split readily along these planes. 



On these delicate surfaces one detects rarely the undulating tracks of 

 worms or the small coriaceous leayes of arctic plants. On other surfaces 

 a delicate ripple marking appeared, regularly arranged — broadly elliptical 

 depressions several inches long and of so slight depth that their presence 

 might easily have been overlooked if they had not been brought out by a 

 film of reddish sand, which filled the hollows and was mostly wanting upon 

 the suiTounding ridges. The depth of the depressions was often only equal 

 to the thickness of a single grain of the fine sand. This surface sand pre- 

 served, also, the delicate water-drift structure impressed upon it by the 

 current. The ripple marks and these drifted sands together registei-, in 

 each case where they occur, a flood so considerable as to give the whole 

 body of water in the lake a current strong enough to enable it to drift 

 along the bottom sheets of the red sands from the border beds farther 

 north out to this i)oint in the very middle of the lake. 



