74 J. D. Dana on the origin of some of the 



d. The sand of the sandy layers is obliquely laminated (not an 

 uncommon fact in such deposits), as shown in the above figure. This 

 division into tliin oblique layers is not apparent when a cut is first 

 made through it with the spade, but appears often on a surface of nat- 

 ural fracture, and very distinctly after exposure for a while to the 

 vdnds. It shows that the sands were deposited in these delicate 

 oblique layers while they were being accummulated in the long or 

 horizontal beds which consist of these. 



e. Throughout the upper part of the section, (above the line N S 

 fig. 1), the inclination in the oblique lamination is mostly to the north- 

 ward: while in the lower part (below NS) it is as generally to the 

 southward. Layers containing both slopes may be observed in each, 

 but the above are the prevalent courses. The formation is thus made 

 up of an upper and lower division ; and in many parts the two are 

 separated by a thin band of large and small pebbles. Near the junc- 

 tion of the Air-line and Hartford tracks, the dividing plain is but two 

 feet above the level of the railroad ; to the eastward it retains nearly 

 the same level (about 22 feet above meantide), but it is higher above 

 the track, there being here a descending grade in the road. Below 

 this bridge, or toward Mill river, the upper division is the only one 

 in sight ; the level of the dividing plain passes beneath the surface 

 of the railroad excavation, and for this reason cannot be traced. For 

 the first two hundred yards on the way toward Mill river, the slope 

 of the oblique lamination rises quite uniformly to the southward as 

 in the upper division above the bridge ; through the next one hundred 

 yards, this is still the prevalent direction ; but farther toward the 

 Mill river end of the cut both slopes occur, and that of the lower 

 division finally becomes the most common. 



f In the upper part, the sands, through the cut for the Air-line 

 road, have the ordinary dirt-brown color ; in the lower part they are 

 hrownish-red. Thus there is a marked distinction between the two 

 divisions in color, as well as in lamination. This color is of course 

 not observable in the pebbly layers. It is owing mostly to the fact 

 that the grains of quartz are tinged outside by red oxyd of iron, like 

 those of the red sandstone. 



The following conclusions flow from the facts here noted. 



(1.) It has already been observed tliat Mill river valley, especially 

 its west side, was the course of a powerful tidal current which set in 

 and out over what is the head of the j^resent harbor, whose ebb was 

 increased by the flow of the river. From the diminution in the amount 

 of pebbles to the eastward of the river (§ a), it appears that the tidal 



