544 GEOLOGY AND MINERALOGY. 
thickness of the strata; in the Appalachians the elevation of the mountains is 
not more than one-fifth or one-tenth even in many places, so that these mountains 
do not give an elevation equal to the thickness of the original accumulations had 
the latter been left undisturbed and simply cut by ravines or watercourses, * * 
Mr. Hall proceeded to say that he regarded the present relations of these 
mountain chains, as well as others, to be not due to elevation along certain lines, 
but that the whole country, whether mountains or plains, is a continental eleva- 
tion; and that the more elevated portions at the present time are due to a larger 
amount and greater thickness of sediment along certain lines,—in other words, 
that mountain elevations are due to original accumulations of sediments along the 
lines of the more powerful transporting currents ; and that the direction of these 
mountains has been determined by the original course of these currents, which 
themselves were determined by a pre-existing cause,—that the foldings of the 
strata and the production of synclinal and anticlinal axes have been produced in 
the instances cited, and doubtless in many or all others occurring on an extensive 
scale, by the subsidence consequent on the great accumulation of material ;—that 
this subsidence and the attendant influences have produced the metamorphism 
which characterizes the strata forming these mountain ranges, and which is every- 
where coincident with their extent.* 
Mr. Hall expressed his belief that the facts before stated as the result of extend- 
ed observations upon a series of strata, and essentially a single mountain chain, 
would be found applicable to many others; and he regarded the laws here set 
forth as applicable to all similiar examples, and as affording a natural and simple 
explanation of these phenomena, for the solution of which unknown and unexplain- 
ed forces had been appealed to as the active agents.” 
SIMPLE RULES FOR CALOULATING THE THICKNESS OF INCLINED STRATA, 
BY E, J. CHAPMAN. 
The following simple rules for calculating the thickness of inclined strata, if 
copied into a blank leaf of the field-book, may prove useful, at times, to some of 
our geological and engineering readers. The results come out in all cases within 
a few inches of the truth. 
Given the angle of dip, and the distance across the beds (i. e., at right angles to 
the line of strike,) required the thickness of the strata. 
(1.) Multiply the dip by 92°15, and multiply the product of this by the distance 
in miles: the resulting product will be the thickness in fee?, 
Or, for short distances: 
(2.) Multiply the dip by 0:01745, and multiply the product by the distance in 
feet : the resulting product will be the thickness in feet, 
Or, when the dip is less than 1°. 
(8.) Divide the constant value (as given above) by the fraction of the degree 
* 
* The author does not deny the influence of other causes acting upon the crust of the 
earth, as contraction, etc., but he considers the effect usually attributed to such agencies, to 
be far too great. 
