Review of Recent Geological Literature. 24i* 
"It appears to me now, even more vividly than it has done in the 
past, that the only agency with which we are acquainted, constantly 
associated with sedimentation and denudation, and capable of these 
enormous dynamical effects, is change of temperature; that expansion 
by increase of heat is the cause of the folding, compression and upheaval 
of rocks, while loss of heat and consequent shrinkage is the cause of the 
earth fractures known as normal faults. This principle I explained 
fully in 1886, in my 'Origin of Mountain Ranges:'' since then the the- 
ory has been subjected to much criticism, ranging from a questioning 
of fundamental principles down to a minor examination of small details. 
'.'The fundamental position has, I maintain, not been shaken, either 
by mathematical physics or geological facts. The more the theory is 
tested by the light of practical geology the more remarkable is the ex- 
planation it affords of the associated phenomena of sedimentation and 
mountain-building, denudation and faulting. Furthermore, no other 
theory yet brought forward attempts to offer an explanation of more 
than one set of these phenomena, namely, those of compression. Nor- 
mal faulting cannot be accounted for by compression, yet the rival the 
ory of tangential pressure on the crust through the shrinkage of the 
earth's nucleus provides for compression only. Contraction, by which 
I have shown that normal faults are produced, is not part of the ma- 
chinery of any other theory than the one associated with my name. 
"I ask geologists to bring to the consideration of these great problems 
clearness of vision, for, usually, a single aspect only is examined, the 
rest beuig left in an impenetrable haze." C. R. k. 
Les Spiriferes dv. < 'oblenzien Beige. Par Ferd. Beclard. (Bull, de 
la Societe de Geologic, de Paleontologie, et d'Hydrologie, tome ix, pp. 
129-210, 5 pis., Nov., 1895.) Few paleontological papers illustrate more 
clearly the modern rebound from the tendency which has existed for 
years past of excessive species making, than does the admirable little 
memoir which M. Beclard has just issued on the spirifers of the lower 
Devonian or Coblenzien group of Belgium. Of the three score forms of 
the genus which have been ascribed to these beds only eight are new 
recognized as valid species. These arc: SpiHfer pvimcevus Steininger, 
S. hystericus Schlotheim, S. subcuspidatus Schnur, S. ardnennensis 
Schnur. S. cultrijugatus Roerner, S. paradoxus Scholtheim, S. dah i 
densis Steininger and $. trigeri de Verneuil. 
The paper is essentially a critical review and revision. All the data 
and reasons for changes in nomenclature arc given at length. If any 
criticism is to be made on the treatment of the subject it would be thai 
it is more prolix than is generally desirable, but this very prolixity is, in 
this case, doubtless necessary in order not to leave the slightest ground 
for questioning the accuracy of judgment in making what will to oaanj 
of those who use the work appear as innovations entirely too radical. 
Seldom does a work appear in which the criticisms are so full of de 
tail, so unbiased in tlieii- treatment and so clcarh set forth in logical 
sequence. Each species is uniformally and symmetrically discussed. 
