ARRANGEMENT OF THE MATERIALS. 9 



been made, may be learned by ascertaining bow near tbe bed of tbe stream we 

 find drift strise and furrows. From some facts of tbis sort, I am satisfied tbat 

 though fluviatile erosion has been considerable in some places, even as much as 

 200 or 300 feet, in general no great amount of the detritus of terraces has been 

 thus produced, except in loose materials. 



Arrangement of the Materials. 



1. Stratification and Lamination. — All these deposits are more or less stratified, and 

 most of the finer varieties are also laminated. The lamination is not unfrequently 

 oblique to the stratification. The former is frequently inclined some 20° to the 

 horizon, tbe latter usually quite horizontal, though the strata or laminae of clay 

 are sometimes plicated. 



The Loess of the Germans, or Limon of the French, along the valley of the 

 Rhine, is usually represented as neither stratified nor laminated. That it is a 

 fresh-water deposit, all admit ; and that the terraces along the Ehine are mainly 

 composed of it, I was assured by Professor Noggerath, of Bonn, as I ascended that 

 river in his company, in 1850. That it is also more or less stratified, I cannot 

 doubt. Indeed, so it is represented by Sir Charles Lyell. But from its composi- 

 tion (fine calcareous clay), we might presume that lamination would be mostly 

 absent. 



The other deposit, apparently without stratification or lamination, is what in Scot- 

 land is called bowlder clay; that is, clay containing pebbles and frequently quite 

 large bowlders. Some which goes by this name in Scotland may be unmodified 

 drift: but where it was pointed out to me, by Dr. Fleming, in Edinburgh, it 

 appeared to be drift modified by aqueous action and deposited in the turbulent 

 waters of the ocean. In this country the clay sometimes so much predominates 

 that it is used for making bricks. I cannot doubt that imperfect stratification may 

 be found in it. 



And here I ought to remark, that when a deposit has been exposed to the 

 weather, even for a short time, all traces of stratification and lamination disap- 

 pear : but when fresh excavations are made in it, both these structures are distinct. 

 By examining many such cuts, made by canals and railroads, I have frequently 

 found the structure beautifully developed where no trace of its parallel arrange- 

 ment could be seen at the surface. Even beds of pebbles, apparently thrown pro- 

 miscuously together, are often found to be arranged in a stratiform manner. 



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, sand, finer or coarser ; at an- 

 other, small pebbles; at another, large pebbles; and sometimes to urge along 

 masses of considerable size. In such cases the stream chose out and carried for- 

 ward the largest pebbles or blocks, which its particular velocity would raise, leav- 



