Mr. Hopkins’s Abstract of his Memoir on Physical Geology. 285 
tions to general laws in the resulting phenomena. It would: 
appear probable however that the time above mentioned will 
be short, and I therefore assume it to be so, and that conse- 
quently the tensions increase rapidly but continuously from 
zero to that degree of intensity which is necessary to over- 
come the cohesive power of the elevated mass. This assump- 
tion has also the advantage of facilitating some parts of the 
mathematical investigation*. 
It will, perhaps, be somewhat more convenient for our 
further investigations, if we conceive the tensions at different 
points of one of our elevated, but still continuous and un- 
broken, component laminz, transferred to corresponding 
points of a plane laminat. For this purpose, imagine each 
point of the curved lamina projected on a plane horizontal 
one, and that the same tension exists at each point of the 
latter, as at the point of the former, of which it is the projec- 
tion; the direction of each tension in the horizontal lamina 
being the projection upon it of that of the corresponding 
tension in the curved one. Now one of our ultimate objects 
will be, to determine the horizontal directions of the fissures 
which must result in the elevated mass, when the tensions be- 
come of sufficient intensity to produce them, and these direc- 
tions may be considered as coinciding with those which would 
be produced in our hypothetical horizontal lamina. Conse- 
quently our investigation will be reduced to the determination 
of these latter directions. 
To elucidate this, suppose our general elevation to be such 
as first mentioned above, or what I have termed cylindrical. 
Its projection on a horizontal plane will be a parallelogram, 
D EK 
G F 
represented by DE FG. Suppose also a partial elevation 
* See Memoir, p. 21. 
+ We may remark that the vertical elevation of the disturbed mass, in 
the state above described, is always extremely small compared with its 
horizontal extent. 
