fe2 An Essay on Rents. [Fkb. 



Of Rents in General. 



There are numerous spaces existing throughout the earth, many 

 of which extend further from its surface towards its cer^tre than 

 man has hitherto penetrated. These spaces contain irregularly- 

 shaped tabular masses of earthy and metallic matter, which have a 

 position very different from that of the matter filling up the other 

 parts of the earth. A close exanoination of all the phenomena 

 presented by these spaces convinces the observer that they have been 

 formed when the matter o*' the earth changed its state from fluidity 

 to solidity, and are owing to its contraction unequally. The most 

 of these spaces, or those which were foiUied the earliest, were 

 filled by some of the matter which is contiguous to their sides being 

 forced into them, from portions of it still nearly in a fiuid state, by 

 the weight of the matter incumbent on these portions ; the rest of 

 thera, or those which were formed when every portion <f the matter 

 contiguous to their sides was so far advanced to its prient state of 

 solidity as to resist tlie incumbent weight, were fillec' with matter 

 that entered thera at the earth's surface, in either a fluid state, as 

 the matter of green-stone, basalt, &c. ; or a solid state, as gravel, 

 sand, and clay. These spaces, therefore, are rents; and maybe 

 called, according to their shapes, the bended-tabular, the straight- 

 tabular, the ovalar, and cylindrical, rents. 



Of the Bended-Tabular Rent. 



In treating of this rent I will, i-n the first part, describe its 

 common names, its shape, dimensions, and position ; the difference 

 in the appearance and position of the strata, between where they 

 are contiguous to it, and at given distances from it ; and, lastly, the 

 forming cause of the rent. In the second part, 1 will describe the 

 arrangement of the matter in rents of this shape ; dividing them 

 into such as contain matter which proceeded from that on their 

 sides, and such as have been filled from above.. 



1. The Names common to this Rent, — Bended-tabular rents 

 which contain only earthy tabular masses, and metallic and earthy 

 crystals, are known by the appellations of slips, dykes, shifts, lodes, 

 troubles, and faults. They are denominated slips by some geological 

 writers, because the strata on one of their sides have slipped from 

 those on the other, and fallen below them. They arc known at 

 Whitehaven by the names of dykes, because they divide the seams, 

 or bands of coal, as they are there called, iuto f eld'). They also 

 call them iip-throw and down-throw dykes ; up-throw dykes, when 

 the strata are higher on the side opposite to that on which the 

 observer is standing; and down-throw dykes, when they are lower 

 on the former than on the latter side. They are called shifts in 

 some parts of England and Scotland, as they are considered by the 

 majority of miners in these parts to have shifted the strata on their 

 •ides. In Cornwall thev are deuomitiatcd cross lodes 5 and in some 



