150 Scientific Intelligence. 



ance in 1897, has filled a unique place, in presenting the relation 

 of surface processes to the destruction and origin of rocks. In 

 this new edition the book has undergone some revision, resulting 

 in the addition of several plates and the cutting down of eleven 

 pages of text. j. b. 



11. Facetted Pebbles. — The article by Lisboa in the January- 

 Journal on " The occurrence of facetted pebbles on the central 

 plateau of Brazil " suggests that there may be a considerable 

 difficulty in discriminating between pebbles facetted by natural 

 sand blast and by glacial action. My experience is that charac- 

 teristic examples of each kind of pebbles may be distinguished 

 without doubt or difficulty. Sand-blast facets usually occur only 

 on one side of a pebble ; in stones of fine grain the facets 

 are ordinarily better made than the facets of glaciated 

 pebbles ; while in stones of coarse grain, such as granites and 

 schists, the facetting often shows a delicate regard for differences 

 of mineral hardness, by which the weaker minerals are slightly 

 excavated or fluted and the harder minerals are left somewhat in 

 relief, in a manner not found on glaciated pebbles. Glaciated 

 facets usually meet in more obtuse angles than those between 

 sand-blasted facets ; and the facets nearly always show striations 

 in sympathy with the longer diameter of the stone ; while stria- 

 tions are characteristically absent on sand-blasted pebbles. 

 Individual specimens of facetted pebbles might sometimes be 

 difficult of identification as to origin ; but a collection of a score 

 or two of pebbles, one set from a district of wind-work, the 

 other set from a bed of till or of tillite (consolidated till), would 

 be easily distinguished. Those shown in Lisboa's paper have 

 decidedly the appearance of sand-blast facets. 



It may be noted that sand-blast facets may be plentifully pro- 

 duced in a district of moist climate, such as the New England 

 coast, provided only that a bed of pebbles is exposed to strong 

 sand-bearing wind. This has happened at various points on the 

 coast of Cape Cod, where facetting of fine quality has been done 

 during the later phases of the glacial period and in the present 

 epoch as well. The occurrence of facetted pebbles in Brazil is 

 of especial interest just at present, in view of Prof. I. C, White's 

 recent account of the extraordinary correspondence between the 

 Permian deposits of that country and those of South Africa, 

 both of which include near the base a sheet of indurated glacial 

 deposits or tillite ; but the pebbles described by Lisboa do not 

 appear to belong to this formation. w. m. d. 



12. Die Kristallinen Schiefer. II Specieller Teil ; von V. 

 Geubenmann. 8°, 175 pp. pis. i-ix ; Berlin 1907 (Geb ruder 

 Borntraeger). — The first part of this work, in which the subject 

 matter is treated from the general standpoint, has been already 

 noticed in this Journal (xix, p. 202.) In this, the descriptive por- 

 tion, the individual kinds of rocks based on the method of classifi- 

 cation adopted, are presented. The chief interest lies in the work- 

 ing out of the method of classification. For purposes of consider- 



