90 
rorULAR SCIENCE REVIEW. 
hydrates, into fully hydrous sesqiiioxide, the reduction of sesquioxide to 
protoxide of iron in the production of green slates, and the exceptional cases 
of the alteration of colour of red beds by the decomposition of bisulphide of 
iron. Eyen the agency of organic matter, in inducing chemical changes in 
the state of combination of the iron, will not, in most cases, account for the 
bleaching — the segregational motion of the colouring oxide — which is the 
ultimate cause of the yariegation, being supplemental to the simple chemical 
changes of combination. Secondly, that the transferrence of the colouring 
oxide from one part of the stratum to another has taken place by the simple 
mechanical agencies of infiltration and dissolution, as well as by segrega- 
tion ; but that the latter, above all other agencies, has played the largest 
part in the yariegation of ferruginous rocks. 
The Qualcrnanj Gravels of England. — From a comparison of the gravels 
of the Aire Valley at Bingley, of the Taff Yale between Quaker’s Yard 
junction and Aberdeen junction, and of the Valley of the Rhonda near its 
junction with the Taff, and of the angles of deposition of gravel-beds con- 
cealing the escarpment of the chalk in the sections exposed at Crayford, 
Erith, and Salisbury, with the same conditions at Brighton and Sandgate, 
Mr. A. Tylor concludes : 1. That the dehris was deposited by land-floods, and 
that the mode of deposition was quite distinct from that of moraines produced 
by the melting of ice. 2. That the character of the deposits in the valleys 
of the Aire, Talf, and Rhonda, proves that they were formed under similar 
conditions. 3. That these givavel-beds point to a Pluvial period of great 
intensity and duration. 4. That the ice action, of which there is evidence, 
was subordinate to the aqueous action. 5. That the fossiliferous quaternary 
deposits have been best preserved where they have been formed in cavities 
lying between the edge of the bank of a river, estuary, or sea, and an 
escai-pment running parallel with it at no great distance. 6. That the 
immediate source of the gravels was the high land adjoining the rivers, 
whence they have been washed down by rain, with the assistance of lateral 
streams, into the lower ground, w’here they had come into contact with 
larger quantities of runnhig water, had been mixed with rolled materials, 
and spread in thick beds over the bottoms and slopes of valleys or the sides 
of escarpments. 7. That the surface of such a deposit rarely slopes at more 
than from 2° to 4°, while the slope of the beds lower in the series nearer 
the escarpment averages 12°. — Quart. Journ. Geol. Soc. Nov. 
tSimilaritg between the Geological Structure of North-westcni Sibei'ia and 
that of Jtussia in Europe. — The following facts have been communicated to 
Sir R. L. ^Murchison by Count A. von Keyserling : The district between 
the rivers Lena and .lenissei is occupied by upper Silurian rocks of the same 
typo as those found in the region of Petchora, and by Carboniferous rocks 
containing seams of coal. Tlio chief secondary' deposits are of Oolitic or 
Ida: ,dc age, and agree witli tliose of the Petchora region, wdiich is the next 
adjacent tract on the west to the Siberian region in question. Similar 
rwks are found in Spitzbergen. 'I’lic banks of the .lenissei are covered with 
post-])liu^enc accinnulations similar to those found near Archangel. It is 
thu.'i seen that the vast, slightly undulating, and to a great extent horizontal 
anfl unbroken fonnations, each of -which occupies so wide an area in 
European Ru.Hsia, are repeated on the eastern side of the Ural Mountains. 
