4 FLORIDA REEFS. 
their steepest shore is turned towards the Gulf Stream, while their more 
gradual slope inclines towards the mud flats which they encircle. 
This is a point which it is important to notice, as it will assist us in our 
comparison between the keys and the shore bluffs of the main-land, as well 
as with the outer reef and the reefs of other seas, in all of which we find 
that the seaward shore is steeper than that turned towards the main-land, 
or, in the case of circular reefs enclosing basins (atolls), than that which 
borders the lagoon. 
The reef proper extends parallel to the main range of keys for a few 
miles south or southeast of it, following the same curve, and never receding 
many miles from it. The distance between the reef and the main range 
of keys varies usually from six to two or three miles, the widest separation 
being south of Key West and east of the Ragged Keys, where the space 
is about seven miles. Between this reef, upon which a few small keys 
rise at distant intervals, and the main range of keys already described, 
there is a broad, navigable channel, extendhig the whole length of the 
reef, from the Marquesas to Cape Florida, varying in depth from three to 
six and seven fixthoms, and, except off Looe Key, where the passage is not 
more than fourteen feet deep at low water, averaging from three to four 
fathoms. 
Farther east the average depth is again the same as at Looe Key ; but it 
becomes gradually more and more shoal towards the east, measuring usually 
about two fathoms, or even less, to the east of Long Key and Key Largo, 
but deepening again somewhat towards Cape Florida, where the reef con- 
verges towards the main keys and the main-land. Protected by the outer 
reef, this channel affords a very safe navigation to vessels of medium size, 
and would allow a secure anchorage almost everywhere throughout tbe 
whole length of the reef, were the numerous deep channels which intersect 
the outer reef well known to navigators, and marked by a regular system of 
signals. As it is, however, the reef seems to present an unbroken range 
of most dangerous shoal grounds, upon which thousands of vessels, as well 
as millions of property, have already been wrecked. These facts have 
a stronger claim upon the attention of the government, since there are, 
as already remarked, numerous passages across the reef which might enable 
even the largest vessels to find shelter and safe anchorase behind this 
threatening shallow barrier. 
The reef proper, as we have remarked above, runs almost parallel to the 
