THE PROGRESS OF GEOLOGY IN l843. xi 
nized on the flanks of tlie Alps and other eruptive continen- 
tal chains^ where the older strata are incumbent on j ounger^ 
and on the western flanks of our own little Malvern Hills,, where 
there is, as before stated, a complete illustration of inverted dip. 
Seeing also, that in proportion as they recede fi*oni the main 
axis the folds are less abrupt, and gradually open out into broad 
and flattened anticlinals, which entirely die away at a certain 
distance from the crystalline and intrusive rocks, or towards the 
interior, the authors form a theory which they conceive to be 
applicable to the bending and elevation of strata generally. 
Comparing the undulations which mark the axes with the 
undulatory motion of the earth during earthquakes, they beleive 
that all the grand ancient flexures of South America were pro- 
duced at one time, and at the termination of the carbonife- 
rous era, up to which period they were all beneath the sea, and 
consequently still in a flexible condition. These sediments were 
it is supposed subjected to flexures by the invasion from below of 
another matter; and the peculiar and numerous convolutions 
are explained by calling into play an upheaving wave-hke oscil- 
lation, accompanied by a tangential or lateral pressui'e upon flexi- 
ble masses which reposed upon a semifluid matter. 
Dr. Dale Owen, has been engaged on the geology of Indiana 
and the Western States. The result informs us that the dis- 
trict between 35° and 43° N. lat. and 81° and 91° W. Ion., 
including the slates of Illinois, Indiana, Ohio, Kentucky, and 
Tenessee,) is composed chiefly of the carboniferous and silurian 
systems.* 
Mr. Lyell, has thrown much light upon the tertiary strata of 
the United States, from Virginia northwards and southwards on 
the sea coast line, and which has been fully reported in the 
Geologist, vol. I. p. 213. and vol. 2. p. 160. The result as already 
communicated to our readers, is his opinion, that the tertiary 
* Geologist, vol. i. p. 251. 
