782 



SCIENCE. 



[N. S. Vol. XXIV. No. 624. 



THE TEUM * COLLUVIAL ' AS APPLIED TO CLAY 

 DEPOSITS. 



While investigating clay deposits in the 

 northern part of Georgia, my attention was 

 called to a large number of recent deposits 

 of some economic value, which were neither 

 residual nor alluvial in origin, and in attempt- 

 ing to classify them the need for a special 

 term was apparent. The term ' colluvial ' is 

 proposed to designate a type of clay deposits 

 which occur in sinks or depressions and at 

 the foot of slopes. The term * colluvial ' is 

 used by G. P. Merrill ^ to include talus and 

 dill debris, and the soil resulting therefrom. 

 By extending somewhat the meaning of the 

 term as used by Dr. Merrill, the particular 

 type of clay deposits in question can be in- 

 cluded under it. The term, in connection 

 with clay deposits, has been very little used, 

 but deserves recognition, both from a scien- 

 tific and economic view point. 



Colluvial clay deposits differ from residual 

 deposits in that they have been transported, 

 and from alluvial deposits in that they have 

 not been carried in suspension by streams and 

 are not flood-plain deposits. They occupy a 

 position midway between residual and alluvial 

 deposits, and may, by gradual transition, pass 

 into either. They are due to the transporta- 

 tion of residual material, by gravity and wash, 

 to the foot of slopes. 



The factors in the formation of colluvial 

 clay deposits are : surface decay of rock masses, 

 producing residual deposits, transportation of 

 this residual material by gravity and wash, 

 and rearrangement by mechanical and chem- 

 ical changes. To illustrate the formation of 

 a deposit take as an example a hill of residual 

 material derived from a crystalline rock. The 

 section of this residue is, beginning at the 

 top, red clay soil containing coarse quartz 

 fragments, yellow to gray clayey residue, dis- 

 integrated rock, and, finally, unaltered rock. 

 By wash by rain water, the finer clay and min- 

 eral particles of the residue are carried fur- 

 thest and lodged at the slope of the hill, form- 

 ing the clay deposit. In granite regions, the 

 clay at the foot of a slope may be almost 



^ * Rocks, Rock Weathering and Soils,' p. 319. 



white, gradually changing into the red and 

 yellow soil higher up the slope. 



An analysis of one of these colluvial clays, 

 from a granite region, is : 



Moisture at 100° 2.462 



Loss on Ignition 8.654 



SiOa (total) 60.110 



SiO, (sand) 31.150 



ALO3 24.256 



Fe.Oa 2.080 



CaO 110 



MgO trace 



MnO trace 



Na-,0 262 



K,0 1.647 



TiO^ 754 



Total 100.331 



Otto Veatch. 

 Geological Survey of Georgia. 



QUOTATIONS. 



'botany m ENGLAND': A REPLY.^ 



In the September number of the Journal of 

 Botany Mr. James Britten deals at consider- 

 able length with the portion of my presiden- 

 tial address to the botanical section at the 

 recent meeting of the British Association at 

 York, which was printed under the title ' Bot- 

 any in England.' 



As Mr. Britten's criticism seemed based on 

 a misapprehension of the drift of my remarks, 

 and as it was printed in a medium often con- 

 sulted by systematic botanists, I naturally sent 

 a reply which I hoped might be inserted in a 

 forthcoming number of the same journal. In 

 his capacity as editor, however, Mr. Britten 

 did not see his way to insert my reply in the 

 form in which I had written it. As I was 

 unable, in my turn, to fall in with the restric- 

 tions imposed by Mr. Britten, hospitality for 

 a rejoinder had to be sought elsewhere. It is 

 under these circumstances that the present 

 note appears in the pages of the Neiv Phytolo- 

 gist. 



Whilst welcoming any criticisms that Mr. 

 Britten may think fit to make, I may, perhaps, 

 be permitted to express the hope that the tone 

 which animates his recent utterance may find 



^ From Neio Phytologist, Oct., 1906, pp. 173-176. 



