66 SECTIONAL ADDRESSES. 
American and British Geologists, for he?* had communicated an instructive 
‘Report on the Geology of North America’ in which he adopted Lyell’s 
Kainozoic nomenclature. In 1842 he read to the Association his joint 
paper with his brother, W. B. Rogers,?? ‘ On the Physical Structure of the 
Appalachian Chain, as exemplifying the Laws which have regulated the 
elevation of great Mountain Chains generally.’ The Rogers considered 
the facts at variance with Elie de Beaumont’s hypothesis that dislocations 
of the same age are parallel to the same great circle of the sphere, as they 
found in the Appalachians nine simultaneous groups of folds which vary 
in trend up to 60°. They explained the folds as waves in the crust due 
to a broad belt being pushed forward with accompanying asymmetric 
folding, overfolding, and inversion. This explanation of fold-mountain 
chains by a wave-like advance of the crust was adopted by J. D. Dana 
for mountains in general. He attributed to the Rogers the first geological 
demonstration of the contraction of the earth, which had been suggested 
by Descartes and Newton. Rogers’ view was confirmed by Bailey Willis*® 
for the Appalachians and adopted for the Alps by Suess in his ‘ Entstehung 
der Alpen ’ (1875). 
Suess showed that the existing physiography of Europe was mainly. 
due to the Alpine System—including the Pyrenees, Alps, Carpathians and 
Balkans—having been pushed northward against resistant masses which 
threw back the waves like forelands along a coast. The Carpathian 
Mountains advanced northward between the resistant masses of Bohemia 
and the Platform of South-Western Russia, as waves sweep forward in a 
bay between two headlands. ; 
Suess in the investigation of mountain structure had the advantage over 
the geologists of the thirties of more certain petrology. They still worried 
over the igneous origin of granite, which was regarded by some of them as 
a metamorphic sediment, and the films of mica in gneiss and micaceous 
sandstone as due to the same cause. Even a decade later the best 
informed petrologists were at issue as to whether granite had been injected 
as a molten mass at a high temperature, or was due to aqueo-igneous 
action at a low temperature. This controversy waged for years between 
Durocher and Scheerer in the Bulletin of the Geological Society of France.?® 
These authors were groping in the dark like physiologists before the 
development of histology. A great advance in the interpretation of the 
igneous and metamorphic rocks was rendered possible by Sorby’s applica- 
tion to them of the microscopic study of transparent sections. He was 
not the first to prepare thin rock slices, which Williamson had used in his 
study of fossil plants. Sorby applied the method to the igneous rocks. 
He®° announced its illuminating results to the Association at Leeds in 1858 
ifi two papers— On a new method of determining the Temperature and 
Pressure at which various Rocks and Minerals were formed,’ and ‘ On some 
*6 Rep. B.A., 4th (for 1834), 1835, pp. 1-66. 
* 12th Rep. B.A. (1842), 1843, Trans., pp. 40-2. 
*° 13th Ann. Rep. U.S.G.S., 1893, p. 228. 
* Ser. 2, vol. IV, 1847, pp. 468-98, 1019-43; vol. VI, 1849, pp. 644-54; 
vol. VIII, 1851, pp. 500-8. 
“0 Rep. B.A. (1858), 1859, Trans., pp. 107-8. 
