466 
NATURE 
[ Sept. 16, 1886 
deprived all at once of its insecure props, settles down to 
a lower level, a forest perhaps subsiding into a lake, or the 
sea over-washing a stretch of shore. 
Slower processes of change, however, are probably 
far more general and effective, and with these seismic 
relations are still in part obscure. Such changes depend, 
there is little doubt, upon variations of equilibrium 
between internal forces of expansion and external forces 
of repression. Where these are accurately balanced, the 
bounding surface of the earth remains unaltered ; where 
subterranean heat gets the better of gravity, as through 
the denudation of large tracts, elevation ensues ; where 
the weight of the superincumbent strata is augmented by 
deposition, there is slow subsidence. The effects of the 
earth’s secular cooling must evidently, in the long run, 
be thrown wholly into the scale for contraction ; and yet 
it is to them indirectly that the upthrusting of mountain- 
ranges is due. These might be compared to the folds 
and creases of a garment grown too ample for the 
shrunken body it covers. The terrestrial crust, indeed, 
is less easily adaptable than an old coat; not a wrinkle 
in it but represents a series of paroxysms, every one 
implying a greater or less amount of earth-shaking, past 
and present. The snap after prolonged strain, the shift- 
ing and twisting of rocks, the fissuring and faulting, the 
slipping and wrenching and grinding of tormented 
strata in the effort to satisfy the stresses put upon them, 
all result in earthquake action of the mechanical kind. 
Thus, mountain-making is essentially a seismic operation, 
not only while in progress, but in its effects during long 
subsequent millenniums. This is one chief reason why 
the lines of earthquake distribution follow so faithfully 
the general direction of mountain-ranges. 
But besides those commotions which result from the 
catastrophic restoration of disturbed equilibrium, there 
are earthquakes of the volcanic or explosive class. This 
species has been defined as an “uncompleted effort to 
establish a volcano.” Such abortive eruptions are 
occasioned, there is much reason to suppose, by the 
sudden formation of steam at great depths beneath the 
earth’s surface. They arise where broken and disjointed 
strata facilitate the percolation of water to volcanic foci. 
A fractured crust and a plentiful aqueous store are 
their developing conditions. Hence their frequentation 
of sea-coasts. Prof. Milne remarks that most Japanese 
earthquakes originate in the Pacific, and that the steepest 
coasts are, on the whole, the most severely shaken ; as is 
easily intelligible when we consider the violence of the 
dislocations necessary to produce them. 
Earthquakes may then be broadly distributed, accord- 
ing to their kind, into two systems, now coalescing, now 
independent of each other. The explosive species 
follow volcanoes along sea-coasts, the mechanical sort 
are associated with mountain-ranges ; all attend lines of 
weakness, and are more or less closely connected with 
the shrinkage by cooling of the terrestrial crust. Thus, 
every volcanic region is liable to earthquakes; though 
there are earth-shaken districts which are not volcanic. 
The tendency to alignment in volcanoes has often been 
noticed: Prof. O’Reilly indicates a similar peculiarity in 
earthquakes, adding that the lines along which they 
range commonly approximate to great circles. This 
inference, or suspicion, can be verified only by detailed 
charting. There are great difficulties, however, in getting 
a true graphical representation of seismic activity. Not 
only deficiencies in records have to be contended with, 
but grave perplexities as to their treatment. They are 
fully admitted by our author. The number of shocks felt 
in a given spot is the criterion inevitably adopted; but 
these may vary to any extent in intensity, or may be the 
mere sympathetic reverberation of some distant cata- 
strophe. The Lisbon earthquake of 1755, for instance, 
may quite possibly have shaken every square foot of the 
globe. The ideal seismic map would be one of earth- 
quake origins, with their attendant areas of disturbance ; 
but this is at present far from being attainable ; and we 
can only acknowledge the indebtedness of science to 
those indefatigable workers who, like Prof. O’Reilly, 
promote knowledge by the best present means open to 
them. 
OUR BOOK SHELF 
Department of Agriculture, Washington: Third Report 
on the Chemical Composition and Physical Properties 
of American Cereals, Wheat, Oats, Barley, and Rye. 
By Clifford Richardson. (Washington, 1886.) 
THIS Report is an important continuation of a most valu- 
able work. The object in view is to obtain accurate 
information respecting the composition of the cereal 
grains produced in the various States. The grain 
analysed is in some cases the produce of seed issued by 
the Agricultural Department, but generally represents the 
ordinary crops of the district. A complete physical and 
chemical examination has been made of each sample of 
grain: the results are tabulated under the head of the 
State in which the grain was reared. The Report con- 
tains 77 analyses of different varieties of wheat grown in 
Colorado; 179 analyses of the kernel of oats, and 1too 
analyses of the husk; 57 analyses of rye, and 72 of 
barley. The extent of variation in composition, the rela- 
tion of physical characters to chemical composition, and the 
influence of climate, are discussed. The results are further 
compared with those obtained by investigations in Europe. 
At the close of the Report are given some detailed analyses 
of cereal grains in which sugar, starch, and the albuminoids 
| soluble and insoluble in alcohol, are separately deter- 
mined. Analyses are also given of the very various pro- 
ducts obtained from wheat by roller-milling. ‘The whole 
is a magnificent contribution to the history of cereals. 
We now know far more of the characteristics of cereals 
grown on the American continent than we do of those 
produced in the United Kingdom. When will an 
English Agricultural Department inaugurate a similar 
study ? ies 
As we have no space for the details of the results, it is 
perhaps hardly fair to criticise. We would merely 
remark that dextrin is not reckoned by the best modern 
chemists among the constituents of barley, or of other 
cereal grains that have been thoroughly investigated. 
The method used for determining starch is apparently 
one yielding too high results, while the “fibre” shown in 
the analyses is far below the total cellulose and incrusting 
matter really present. We call attention to these errors 
of method, as they are very generally met with, and it is 
high time that they were remedied. R. W. 
Longmans’ School Geography. By George G. Chisholm, 
M.A., B.Sc. (London: Longmans, Green, and Co., 
1886.) 
ONE point which the recent discussions with regard to 
geographical education in this country has brought out 
en 
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