220 Dr. Richardson's Letter on the basaltic Surface 
We meet still more frequently an imperfect style of hum- 
mock, a semi-circular fa9ade on one side, while on the other 
it slopes away gradually with the dip of the strata, as if the 
operation had been interrupted before it was carried quite 
round ; the most remarkable of these are Ballystrone, in Derry, 
and Croaghmore , in Antrim, both visible from Dunmull. 
Regular stratifications on the summits of hills and moun- 
tains, have been long a stumbling block to theorists ; the his- 
torian of the French Academy, for the year 1716, obviously 
ascribing the superficial inequalities of the earth, (like many 
others) to causes acting from below, and perceiving how in- 
compatible such assemblages of strata were to his theory, 
thinks it safer to doubt their existence, as they could not have 
been formed, he says “ unless the masses of the mountains 
‘ s were elevated in the direction of an axis perpendicular to the 
“ horizon : ce que n’apu etre que ires rare.” 
But as these stratified mounts are in our area by no means 
uncommon, they lay us under the necessity of suggesting- 
another alternative similar to those we have already stated. 
Were these isolated hummocks originally formed as they 
now stand, (solitary and separate from each other) one by 
one ; or, are they the last remaining portions of a vast conso- 
lidated mass, of which the intermediate and connecting strata 
have been carried off by causes with which we are unac- 
quainted ? 
To be able satisfactorily to resolve this alternative, it be- 
comes necessary to take a careful view of the contiguous 
countries, and to try whether their construction, and the ar- 
rangement of their strata, will throw any light upon the 
subject. 
