CAUSES OF DISTURBANCES, CtC. 
633 
effected; such as we see have been produced in the crumpled strata of the Apalachian chain, 
and in its continuation through and across the Hudson valley, the Green mountains, etc. ; 
and as the points on the surface would be more affected than those nearer the centre of the 
revolving system, the wrinkles and folds of the strata would all have a tendency to fall over 
to the westward, giving an eastwardly dip. 
If the changes of diameter of the earth, and consequently of the day, have been secular 
and not paroxysmal, the same principles would hold true, but the effects would necessarily 
be less marked. 
We have no evidences of changes of longitude or of the length of the day during the 
historical era; but we have geological evidences of changes of longitude on many parts of 
the earth’s surface, in the wrinkling, crumpling and crushing of strata, the elevation of 
extensive mountain ranges, and the lateral heaves of transverse joints throwing the strata, 
and even the hills and mountains, in echelon. We have also evidences of stronger currents 
having existed in the ocean at particular periods than at others. 
All these effects may be referred to the secular refrigeration of the globe, collapse of the 
exterior upon the interior, either paroxysmal or secular, diminishing the mean diameter, 
though often elevating portions of the earth above its former relative level; and also a lateral 
tangential force acting like that by collapse, only always in a westward direction. 
It has been ascertained that the day has not varied in length a three hundredth of a cen¬ 
tesimal second during the last two thousand years, and we have no geological evidence of 
any change during more than four thousand years; and all the changes that are as yet 
capable of being rendered at all certain, date back to periods far— far more remote. 
Supposing a diminished radius of the earth corresponding to one three hundredth part of a 
second variation in the length of the day, the westward daily tendency from altered velocity 
would be so small as to be supposed unworthy of consideration; but it is to be observed, 
that this inertia acts continually, until the moving mass acquires the increased velocity, and 
in the course of time, the strata being supposed to yield along the lines of least resistance, 
the changes of longitude on points of the moving mass might be expected to become manifest. 
M. Laplace has estimated the influence that the planetary bodies would have upon the 
length of our day, and shown that it would amount to only a few minutes in many millions 
of years; but I believe that the influence of refrigeration and contraction has not yet been 
calculated, and it is a subject worthy of investigation by some of our mathematicians. 
