ABKANGEMENT. 97 



Sometimes there is a structure like cleavage present. Fig. 40 represents a section in a terrace at Bartons- 

 ville (Kockingham.) It is represented as Terrace No. 4 upon the map of the Surface Geology, Plate II., 

 and upon Plate VII., Fig. 1, where an enlarged map of s. Fio. 46. N. 



some terraces upon Williams Kiver is given. Its place is Ao 

 easily found on these maps by. noticing the point where this 

 terrace curves and*erosses the valley. By an excavation 

 made for the Kutland and Burlington railroad, and by the 



action of a powerful freshet recently, a large part of the 



/v / i Section in a Terrace at Bartonsville. 



terrace was worn out, leaving elms ot clayey sand exposed 



on either side. It is from the cliff upon the east side of the railroad track that this figure is taken.* A A 

 represent two strata, each about three inches in thickness, composed of numerous laminas. a a a a B 

 represents a stratum six inches in thickness, composed of lamina?, a a, like A A. In addition to these lines, 

 the action of the weather has brought to light another system of planes b b, dipping at an angle of fifteen 

 degrees to the north. They protrude from the surface of the cliff very much as segregated veins are elevated 

 above the surrounding mass of rock upon blocks of stone where the weather or drift agencies have been at 

 work. It is not a laminated structure, for the laminse are horizontal ; which position is very clearly shown 

 by little scales of mica lying upon their flat surfaces, and moreover the dip is in the wrong direction to sup- 

 pose them formed by deposition. The dip is to the north, while the current of deposition acted from the 

 north to the south ; and were these planes laminae, they would dip to the south. It seems to be analogous 

 to a cleavage structure; though it may not cleave in- the direction of these planes so easily as in the direc- 

 tion of the planes of lamination. It would certainly lead us to inquire whether cleavage planes may not be 

 formed withoul the aid of heat and pressure, by some simple agency in operation at the present day. 



Certain deposits of the age of terraces, and in many cases forming terraces, are repre- 

 sented by some geologists as neither stratified nor laminated. Such a deposit is found 

 along the valley of the Rhine, and is called loess by the Germans, and limon by the 

 French, and upon the Mississippi River, in America, in the bluffs. Doubtless the stiff 

 clays of the Champlain valley at times possess the same indistinctness, for their composi- 

 tion is the same as that of the loess, viz: fine calcareous clay. We have never seen a case 

 where stratification was wholly obliterated, though it is often quite indistinct. And 

 it should be observed here that when a deposit has been exposed to the weather, even 

 for a short time, all traces of stratification and lamination may disappear : but when fresh 

 excavations are made in it, both of these structures are distinct. The numerous cuts made 

 by railroads display the structure of terraces in many cases very finely, where no trace of 

 parallel arrangement can be discerned upon the surface. In this way stratification may 

 be seen in beds of pebbles, apparently thrown promiscuously together. 



2. Sorting. Wherever a section is made into a terrace, composed of clay, sand and 

 pebbles, we see that these varieties of material are usually arranged in distinct layers, the 

 coarser together, and the finer together. The impression is irresistible on the mind, that 

 the water, which made the deposit at one time, had only velocity sufficient to move the 

 finest sediment ; at another, small pebbles ; at another large pebbles ; and sometimes to 

 urge along masses of considerable size. In such cases the stream chose out, and carried 

 forward the largest pebbles or blocks, which its particular velocity would raise, leaving 

 other fragments for a time when its power should be increased. In this way have the 

 materials been sorted out more nicely than any mechanical skill could have done. 



*In 1860 this cliff was nearly gone. It will be entirely gone in two or three years hence. 



