838 



DYNAMICAL GEOLOGY. 



4. By means of migrating animals, p. 607. 



5. By the help of floating logs or living plants, p. 607. 



5. Deposition and Arrangement in Beds of Fragmental Material. 

 — 1. By winds, p. 631. 



2. By fresh waters in their ordinary condition, or during occasional or annual floods, 

 pp. 654, 658. 



3. By fresh waters in a prolonged flood, producing till, p. 546. 



4. By a plunging flow of waters, pp. 546, 685. 



5. By marine waters, p. 680. 



6. By glaciers or icebergs, p. 698. 



6. Organic Contributions to Fragmental and other Deposits. — 

 1. Of a Calcareous nature, pp. 59, 60, 135, 615, 707. 



2. Of a Siliceous nature, pp. 59, 60, 135, 708. 



3. Of Excrementitious origin, or phosphatic, pp. 59, 60, 613. 



4. Of Carbonaceous character, pp. 60, 61, 612, 616. 



7. Colors of Fragmental Deposits, Limestone included. — 1- Brown- 

 ish-yellow to brown colors due to limonite, the hydrous oxyd of iron, Fe 2 3 -+- l^HO. (1.) 

 The limonite derived directly from the oxydation attending the disintegration by which 

 the sands were made, the sands having not been subjected afterward to washing on a 

 seashore, which removes such iron-oxyd. 



(2.) The limonite deposited in a low wet region, where the fragmental deposit was 

 in process of accumulation ; not a possible result in an open estuary or on an open coast, 

 p. 710. 



(3.) The limonite produced by the action of ordinary waters on a deposit, pervious to 

 water, containing an iron-bearing mineral, p. 710. 



2. Brownish yellow or brown color, due to the hydrous iron-silicate, palagonite. This 

 mineral is formed when a bed of volcanic cinders or granulated volcanic rock is sub- 

 jected to the action of warm waters, the pyroxene of the material being altered, by 

 losing part of its silica, having its iron changed to the sesquioxyd state, and taking in 

 water. 



3. Green, Brownish-green, or Olive-green color, due to the hydrous iron-silicate, glau- 

 conite. — The silica in glauconite, the green mineral giving the color to the green-sand 

 of the Cretaceous and other formations, is supposed to come from the siliceous secretions 

 of minute Sponges in the cellules of Bhizopods, etc: but the process of formation is 

 not understood. 



4. Bed color, due to red oxyd of iron, Fe 2 3 . — (1) From the heating of beds con- 

 taining limonite as the coloring material, limonite becoming the red oxyd when heated, 

 p. 764. 



(2.) From the oxydation of the iron of an iron-bearing mineral through the action of 

 moisture and heat, pp. 711, 764. 



(3.) The same as (2), at the ordinary temperature in dry warm regions. 



5. Black and Brownish-black colors.— -(1.) From the presence of carbonaceous sub- 

 stances, derived from vegetable or animal matters ; in which case the rock will burn 

 white. 



(2.) From the presence of an oxyd of iron; in which case the rock will burn red. 

 (3.) From the presence of an oxyd of manganese ; in which case the rock will remain 

 black or bluish-black, on heating. 



6. Mottled Coloring. —1. Rocks colored red or brownish-red, with oxyd of iron, be- 

 come mottled, through the deoxydation of the iron, by means of waters containing 

 organic matters : the waters often pass through loose sandy beds without altering them, 

 and then reach a clayey layer where they spread and make the changes, p. 710. 



7. External colors due to vegetation. — Minute black, brownish-black, and greenish- 

 gray lichens give an external coloring to rocks, which is often mistaken for their true 

 colors. Outcrops of granular limestone, a white rock, are usually quite black, from 

 the species with which they are overgrown. Larger lichens sometimes spread over the 

 surfaces of rocks, and give them a mottled aspect. 



