222 Dr. Richardson 3 s Letter on the basaltic Surface, &c. 
operations and modes of acting, we have hitherto obtained 
little knowledge. 
The highest point on the facade of Cave Hill is called 
M‘ Art’s Castle, and appears to be a solitary fragment of a 
stratum, precisely similar to those below it, and obviously 
once extended like them. 
The irregularity of the summit of Fairhead , plainly shews 
that its gigantic columns once reached higher. 
And in the facade of Magilligan, the highest of all, a few 
desultory patches of an upper stratum ( no doubt once perfect 
and continuous ) are to be traced along its summit. 
Our mountains themselves seem to shew clearly that they 
were once higher ; the top of Magilligan mountain is an ex- 
tensive plain, over which a wandering stratum is interrupted 
and resumed at intervals for a great way. 
At the highest part of Donald’s Hill, over the valley of 
Glenuller, we find a hummock ; also at the termination of the 
ridge, at its highest part over the valley of Mayola, similar 
hummocks. 
I have the honour to be, 
Sir, 
Your obedient, humble Servant, 
W. RICHARDSON. 
Clonfede, fan. 2, 1808. 
