2 i c 2 Dr. Richardson's Letter on the basaltic Surface 
mineralogists called a porphyry, the mass friable, but the com- 
ponent angular particles of extreme hardness. 
The hills, of which this little district is full, are every one 
perfect segments of spheres, while the loftier basaltic hills 
that surround it preserve their characteristic form, to wit, a 
gradual acclivity on one side, with a steep abruption on the 
other. 
As we sail along; our northern shore we discover another 
great chasm or interruption of our strata, which also cuts 
deep into the substrata : for on the west side of Bally castle 
pier, the bold basaltic precipices suddenly disappear, and at a 
lower level disclose the substratum, which appears to be an 
alterpgtiqp- of sand-stone, and coal, sometimes with bitumi- 
nous schistus. 
A mile or two to the eastward the abrupt precipice is 
resumed, and a basaltic stratum again occupies its summit on 
to Fairhead, with the same angle of inclination in which it was 
disposed along our whole coast, that is, a slight ascent to the 
north. 
Traces of similar operations and abruptions are to be found 
over our whole area, but the preceding are sufficient to make 
us acquainted with the style of these interruptions of our 
strata ; of course it is time to proceed to the suspended de- 
monstration, that our strata, so interrupted, were once conti- 
nuous, notwithstanding the magnitude of the interval by 
which the corresponding parts are now separated. 
