si 
‘ ADDRESS. xiii 
analogous to the three known states of carbon, to which they are thus closely 
allied, namely charcoal, graphite, and diamond. ‘The last of these states is, 
of course, the most interesting. Crystullized boron possesses a hardness, 
brightness, and refractive power comparable to those of diamond; it burtis 
in chlorine, without residue, and under circumstances resembling those of 
the combustion of diamond in oxygen; it is not acted on by any of the acids, 
and appears to be the least alterable of all the simple bodies: I have been 
informed that its powder is already used in the arts, instead of diamond dust; 
and it seems not improbable that, when obtained by the chemist in crystals 
of larger size, it may rival the diamond as a gem. 
The science of Geology appears, of late years, to have entered upon a new 
phase of its development,—one characterized by a stricter reference of its 
speculative views to the principles of those sciences with which it is con- 
nected, and upon which it ought to be based. The able memoirs of Mr. 
Hopkins, on what may be called dynamical geology, afford a remarkable 
proof of this ; and we have another instance of the application of sound phy- 
sical principles to this science in the explanations which have been recently 
offered of the phenomena of slaty eleavage. A Report on this interesting 
subject was presented to the Association by Professor Phillips at its last 
Meeting, and will be found in the volume just published. These sounder 
views originate, I believe, with himself and with Mr. Sharpe; but they have 
been enlarged and confirmed by Mr. Sorby, Dr. Tyndall, and Professor 
Haughton. 
We have an interesting proof of the readiness of geologists of the preserit 
day to submit their views to the test of exact observation, in the meastire- 
_ ments undertaken by Mr. Horner for the purpose of approximating to the 
age of the sedimentary deposits. Of the geological changes still in opera- 
tion, none is more remarkable than the formation of deltas at the mouths of 
_ great rivers, and of alluvial land by their overflow. Of changes of the latter 
_ kind, perhaps the most remarkable is the great alluvial deposit formed in the 
valley of the Nile by the annual inundations of that river; and here it for- 
tunately happens that history comes to the aid of the geologist. These sedi- 
’ mentary deposits have accumulated round the bases of monuments of known 
_ age, and we are therefore at once furnished with a chronometric scale by 
_which the rate of their formation may be measured. The first of the series 
_ of measurements undertaken by Mr. Horner was made, with the coopera- 
tion of the Egyptian Government; around the obelisk of Heliopolis, a monu- 
ment built, according to Lepsius, 2300 years B.c. A more extensive series 
of researches has been since undertaken in the district of Memphis; but 
3 Ir. Horner has not yet, I believe, published the results. 
__ The problems now to be solved in Paleontology are clearly defined in the 
enunciation of the problem recently proposed by the French Academy of 
Sciences as one of its prize questions, viz. “ to study the laws of distribution 
