45 
Most Geologists are agreed, that the abundance of organic re- 
mains in the limestone rocks show them to have been, at some for- 
mer period, the residence of animals. Nay some have gone so far 
as to suppose, that these rocks are entirely composed of the remains 
of the animals of a former race, consolidated together by the effect 
of subsequent revolutions of the globe. In either way, the posi- 
tion of the great shell beds before mentioned bears a singular ana- 
logy to the situation ofthe limestone strata, which covers so large 
an extent of Ireland; and it might perhaps be possible to discover, 
by a careful examination of the shelly remains, whether they are 
portions of the petrifactions from a limestone rock abraded by the 
action of the sea, or the exuvize of animals now in existence. In 
the mean time, it is proper to observe, that no other so remarkable 
a bed of shelly matter occurs elsewhere in the Irish sea, or until you 
get beyond the northern straits into the Atlantic ; nor do I know of 
any so remarkable in the north sea, though the nature of its bottom 
appears to have been carefully investigated by pilots. 
In the British channel however, there is another extensive tract 
of this nature occupying the centre of the space between England 
and France, and for many miles to the westward while you keep 
south of Scilly ; but, to the north of Scilly, the bottom is of an en- 
tirely different nature. 
Nothing is more interesting to Navigators, on their way home from 
the Atlantic to our coasts, than the means of distinctly ascertaining 
their position on approaching the land. In thick weather, when 
astronomical observations are not to be had, and when, from the 
influence of unknown currents or the like, the reckoning may be 
justly suspected, it is of the utmost consequence to keep the ship in 
the fair wayof the channel, 
Experienced pilots allege, that this may be known by the nature 
