Correspondence — Mr. T. Mellard Reade. 571 



niatliematical matter in an appendix ; and secondly, the natural 

 sequence adopted for the crystallographic systems, from the simplest, 

 viz. the Anorthic, to the most complex, the Cubic. This step, 

 analogous to that which makes our modern geologists and biologists 

 commence with Laurentian, Protozoa, and Protophyta, is one of the 

 greatest philosophical importance. Had space permitted it, we 

 should have liked a little more information on crystallogenesis, more 

 references to the history of the science, a description of the Eeflective 

 Goniometer of WoUaston, and more detail in chapter xvii., which 

 treats of ' the Physical Symmetry of Crystals.' In a subsequent 

 edition we may suggest that the italicizing of all technical terms 

 when they first occur should be more uniformly carried out, that 

 more references to figures be inserted in the text, and that the dia- 

 grams for finding the symbol of a zone when those of two faces are 

 known, and for finding the symbol of a face common to two zones, 

 on pp. 23, 24, be made clearer. The term 'holohedral forms', 

 though mentioned in the index, is only defined by implication ; 

 ' deutosystematic ' on p. 72 should, we presume, be ' deuterosyste- 

 matic;' and Naumann's Method of Projection is only attributed to 

 him in the ' Contents ' ! ^ We would particularly call students' atten- 

 tion to the excellent series of terms proposed by Professor Maske- 

 lyne, given on p. 54, and to Mr. Gurney's triumphant proof, on 

 p. 59, that the three rhombohedral planes of symmetry represent the 

 holohedral type of the system, and that the double six-sided pyramid 

 is merel}' a combination of two rhombohedra. We sincerely con- 

 gratulate the author on his useful contribution to science; and can 

 only regret that the majority of those pupils whom he has, during 

 some years, instructed in the substance of this work, have gone to 

 India in a capacity in which science can only be the hobby of hard- 

 worked men ; so that we can hope for but little fruit from their 

 knowledge of crystallography. G. S. B. 



coE,E,:E]si=03iTXD:E3sro:Hi. 



CLAY BOULDEES. 



Sir, — An interesting phenomenon which may assist to explain the 

 structure of certain argillaceous rocks is now to be observed on the 

 Crosby shore near the Kiver Alt. 



Some time since a trench had been out in the blue clay, which 

 underlies the Peat and Forest Bed,- in a south-westerly direction 

 across the shore. For many years this trough, though filled by the 

 tide at springs, has remained open, with simply a deposit of sand on 

 the bottom. I have not measured it, but I should judge the trench 

 to have been about fifty yards long, five feet wide, and two feet 

 deep. At the present moment it is filled up nearly to the surface 

 with an agglomeration of rounded lumps of clay more or less com- 

 pacted together. The clay boulders, for such they are, vary in size 



^ WTiere his name even is mis-spelt. 



^ See '• The Submarine Forest at the Alt Mouth," Quart. Joum. Geol. Soe. vol. 

 xsxiv. pp. 447-8, and other papers therein referred to. 



