Darwin mentions Belize (Honduras at that time) in his 1842 book: “The structure and distribution of coral reefs. Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836”http://darwin-online.org.uk/content/frameset?itemID=F271&viewtype=side&pageseq=219
The islets on it are all low, as I have been informed by Capt. B. Allen; the water deepens suddenly on the outside the reef, but not more abruptly than off many of the sedimentary banks: within its southern extremity (off Honduras) the depth is 25 fathoms; but in the more northern parts, the depth soon decreases to 10 fathoms, and within the northernmost part, for a space of 20 miles, the depth is only from one to two fathoms. In most of these respects we have the characteristics of a barrier-reef; nevertheless, from observing, first, that the channel within the reef is a continuation of a great irregular bay, which penetrates the main land to the depth of 50 miles; and secondly, that considerable spaces of this barrier-like reef are described in the charts (for instance, in lat. 16° 45 ' and 16° 12 ') as formed of pure sand; and thirdly, from knowing that sediment is accumulating in many parts of the West Indies in banks parallel to the shore; I
have not ventured to colour this reef as a barrier, without further evidence that it has really been formed by the growth of corals, and that it is not merely in parts a spit of sand, and in other parts a worn-down promontory, partially coated and fringed by reefs: I lean, however, to the probability of its being a barrier-reef, produced by subsidence. To add to my doubts, immediately on the outside of this barrier-like reef, Turneffe, Lighthouse, and Glover reefs are situated, and these reefs have so completely the form of atolls, that if they had occurred in the Pacific, I should not have hesitated about colouring them blue. Turneffe Reef seems almost entirely filled up with low mud islets; and the depth within the other two reefs is only from one to three fathoms.