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Assistant Bolles commenced this work in February, and closed operations in May; he was assisted in it by sub-assistant George A. Fairfield, and during part of the season by S. S. Pendleton, esq. It was carried on under disadvantageous circumstances from the illness of Mr. Bolles, and yet presents a considerable amount of work. The area embraced is 35 square miles, 12 stations were occupied, and 115 angles measured, on 24 objects, by 978 observations, with a six-inch repeating theodolite by Gambey, (C. S. No. 35.) Soon after closing this work, the services of assistant Bolles were called for, to execute the secondary triangulation, already referred to, at the entrance to Cape Fear river, North Carolina. He is now under instructions to complete the triangulation of the Savannah river, alread commenced, and to carry the work, which has just been described, southward and westward, towards Beaufort, South Carolina. Topography.—Assistant George D. Wise was engaged, with a planetable party and the surveying schooner Franklin, upon the topographical survey of North Edisto river and harbor of refuge, South Carolina, from February 12 to April 18, when himself and party were transferred to the seacoast of Virginia. He was aided by J. A. Denny, esq. Both shores of the river are embraced in this survey, (sketch E, No. o which covers 40 square miles in area, and extends along 100 miles of shore-line and 44 of roads. The base measured in 1850 on Edisto island furnished marked points, which were made available for the topographical survey. Sub-assistant S. A. Wainwright, with another party, during the two months ending June 7, was employed in the topographical survey for a harbor chart of Savannah river. His work has established the points used by Lieutenant Commanding Maffitt, United States navy, for the hydrography—from Elba island to Argyle island, on both sides of Hutchinson's island, including eight and a half miles of shore-line; from Elba is'and to Savannah city, (comprising the wharves,) on the south side of the river; and from Elba island to a little below the south base signal on the north side, (see sketch E, No. 2.) From this section Mr. Wainwright and party were transferred to work along the eastern shore of Virginia. Hydrography.—Lieutenant Commanding J. N. Maffitt, United States navy, with the Coast Survey schooner Gallatin, (after being a few days employed in Section IV,) returned to this section December 12, 1850. He resumed the survey of Charleston bar and approaches, and in about one month completed the soundings requisite for the chart of that harbor. Thence he passed to North Edisto inlet, South Carolina, and, after much interruption from boisterous weather, finished, March 5, 1851, the hydrography of that river and bar, (sketch E, No. 7.) In the Appendix (No. 30 tris) are sailing directions, which have been published, furnished by Lieutenant Commanding Maffitt, for the entrance into that harbor of refuge. “It is about sixteen miles to the southward and westward of Charleston light-house, and is easy of access, one course over the bar taking the vessel to a safe anchorage. At mean low water there are thirteen feet on the bar. The mean rise and fall is six feet.” The hydrographical reconnaissance of Savannah bar and river was next undertaken; the shore parties co-operating being furnished with a boat's crew from the vessel. The work, completed June 4, extends from one mile outside of the outer bar buoy, embraces the “Main,” “Front,” and “Back” rivers, and terminates at Argyle Tree, six miles above the city of Savannah, (sketch E, Nos. 4 and 5.) The statistics of the work in this section are as follows:

Number of observations of angles. . . . . - - - - - - - - - - - - - - - - - - - 2,069 Number of soundings---------------------------------- 60,001 Miles sounded over--------------------------------- - - - 1,237 Number of specimens taken of bottom- - - - - - - - - - - - - - - - - - - - 95 Number of sets of current observations......... - - - - - - - - - - 14

From the Savannah river Lieutenant Commanding Maffitt returned to Section IV; and, after necessary delays for repairs of vessel and, shipment of a crew, entered on the reconnaissance of the bars of Smithville and New river, North Carolina. A permanent tide-gauge was erected at Fort Pulaski, entrance of Savannah river, where careful observations, day and night, of the tides have been regularly made since January. A permanent tide-gauge has also been erected at Castle Pinkney, in Charleston harbor; but circumstances have not heretofore permitted tidal observations to be made with the same regularity. At North Edisto inlet the tides were observed, day and night, for eight weeks. Besides their field-work, Lieutenant Commanding Maffitt and party have completed and turned in the following office-work, in mapping their results, viz: A chart of Charleston bar and harbor. Another of the same bar and approaches, with additional work on Rattlesnake shoals, which was off the limits of the original sheet. A chart of Savannah bar, from one mile outside of the outer bar buoy to Cockspur. One of Savannah Main river, from Cockspur to Shad's Chimney. Another of Savannah Front and Back rivers, from Shad's Chimney to Argyle Tree. A chart of North Edisto bar and river. Charts of Beaufort, North Carolina, bar and harbor. Lieutenant Commanding Maffitt renders acknowledgments for the courtesy and facilities extended to him, while employed in Savannah river, by the officers of the army there stationed.

Section VI.-FRoM THE st. MARY's River to st. Joseph's BAY, coAst of FLORIDA, AND INCLUDING THE FLORIDA REEF AND KEYS.—

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The work on this important and comparatively ill-known portion of our coast has been pushed vigorously, as far as the appropriation permitted, in all its branches. The land parties have had in use three vessels belonging to the coast survey, or hired for the purposes of transportation; and the hydrographic party the Coast Survey steamer Hetzel, which had been put in thorough repair after the accident of last Canaveral. Four parties have thus been in the field, en

year at o: gaged on the main and secondary triangulations, the hydrography and

topography of those keys and reefs where the need of information was most urgent. It should be remembered that the appropriation recommended by the Treasury Department in 1848–49 ... speedy survey of this section, was reduced from $100,000 to $30,000, and that the present limited scale of work merely provides for the ordinary rate of progress. Even as it is, however, the knowledge aequired and now ready for publication will be of no small value towards the saving of life "W. So often lost or perilled on this coast. The habors of Key West and Cedar Keys, the passage of the Boca Grande, and many of the smaller keys and reefs, have been thoroughly examined and mapped; mistakes of charts in present use rectified; and determinations made for the sites of lights and buoys indispensable to the safety of navigation. Accompanying this report are—the general sketch F, showing the progress of work, in this section; sketch F, No. 2, showing on a larger scale the rogress of Cedar Keys, Dry Tortugas, Key West, Bahia Honda, and Key Biscayne; sketch F, No. 5, of the harbor of Key West and its approaches; sketch F, No. 4, of the harbor of Cedar Keys, with Suwannee bay to the northward and westward, and Wacassassa bay and the harbor and offing of Crystal river to the southward and eastward; and sketch F, No. 3, of Mosquito harbor. The new channel at Key West, mentioned in my last annual report as indicated by the work for that season, has been found to afford a depth of 26 feet. The depth that can be carried through the passage of Boca Grande is ascertained to be 13 feet. Into Cedar Keys bay it is found that, by the main channel under Sea-horse key, 12 feet can be brought in, and, perhaps, under favorable circumstances, 14. Examination has confirmed the vaguely reported existence, off Crystal river and below Cedar Keys, of a harbor and anchorage (in the bay now called St. Martin's, just south of the Withlacoochee river) into which 12 feet, and, under favorable circumstances, 14 feet of water may be carried; and which will be valuable not only as a shipping port for the produce of several neighboring rivers, but as a place of refuge for coasting vessels. It may be remarked, as a matter of general interest, that the survey indicates Way key as the most desirable and, indeed, the only suitable terminus for the railroad across the peninsula. The anchorage at Crystal river being at some distance from the main land, renders that pointineligible; besides, that the route would be over rivers and marshes to reach it. Professor Agassiz has lent the aid of his distinguished talents in an examination, the results of which are embodied in a report discussing the topography of Florida, its reef, keys, coral reefs (living and dead.) ship-channel, main land, coast, and the physical changes in the Gulf Stream. Apart from the fact that this report would be too much extended by including that document, its importance requires that I should make it the subject of a special communication. This examination was imperiously called for by the contradictory statements in regard to the character of the reef in its different portions, being by some represented as composed of living and growing coral—

by others of boulder masses of dead coral; sustaining, in the two cases, altogether a different relation to navigation, and to the questions of sites for light-houses and sea-marks. The very interesting question of the past growth of the Florida reefs and the formation of the present peninsula of Florida, and of the keys which form such remarkable appendages to it, has been fully solved by Professor Agassiz, who has also shown what may be expected in the future; and, establishing the fact that the existence of the coral depends upon the depth of the sea, proves that no reef is to be expected exterior to the one existing.

This, of course, supposes that no change occurs in the relative level of the land and water; and here, again, the labors of Professor Agassiz have been in the highest degree valuable, by establishing that no general change of this kind is going on in that part of the coast; the phenomena of growth of the reef, formation of the keys and of the main land, being explicable without such supposition. I have extracted such portions of the report of Professor Agassiz as bear most immediately upon the subjects of my present report, in the Appendix No. 10; but the whole work is too valuable to permit any portion to be lost, and I therefore respectfully recommend that it be presented to Congress by the department in a separate report.

Hourly observations of the tides near Key West have been made under my instructions, and the immediate direction of Lieutenant Commanding John Rodgers, United States navy. They have been plotted, and are in course of reduction and discussion, in the same manner as those at Cat island, Louisiana. The results are of great interest in reference to the general subject of tides in the Gulf of Mexico; but the investigation is, perhaps, in its present stage, too purely technical to make an extended notice desirable in this report. There are two high and two low tides daily at Key West; the successive tides being nearly equal about the time of the moon's passing the equator, and there being at other periods one smaller and one larger tide in the course of the twenty-four hours. This diurnal inequality is a very remarkable feature, and can already be approximately calculated.

The work of this section will be resumed as early as arrangements can be made for the ensuing season.

Reconnaissance, triangulation, $c.--Assistant F. H. Gerdes has been occupied (with the exception of a brief absence on duty in Section VIII) from November 1st, 1850, to June 20th, of this year—first, in reconnaissances, having for their object to select stations for the main triangulation, and to connect the Tortugas with the main body of the work; second, in preparing, clearing and grading a base line on Key Biscayne, and another at Cape Sable; third, in the establishment of stations, main and secondary, and in the triangulation.

The description of the coast and other information conveyed in Mr. Gerdes' report of a reconnaissance, which extended from Suwannee river to St. Martin's reef, are of so much interest that I annex the report nearly entire. (See Appendix, No. 31, and sketches F, Nos. 1 and 4.)

Mr. Gerdes has found that, by fixing a signal upon Rebecca shoal, about midway between the Tortugas and the Marquesas, the former group mạy be brought into connexion with the general scheme of main

triangulation. This plan involves less time and expense than those previously suggested, and dispenses with the use of reflecting instruments and of floating signals. A short base must be measured on the Tortugas, and an astronomical station for azimuth observations be made there. In that group, the triangulation from the Logger-Head base will furnish a proper side of nearly five miles, and a distance of four miles may be had at the Marquesas from the eastern triangulation. The base lines, referred to in my last annual report, have been cleared with some labor, levelled, and well prepared for measurement. (See sketches F No. 3, and F No. 4, report of 1850.) In the triangulation of this season 30 signals have been put up, and determined from 11 stations, forming 41 triangles, and embracing the whole of the harbor, with all four channels of the Cedar keys, and the islands themselves. A small preliminary base of about two miles was measured on Way key by chaining, and the ends, as well as all the stations of the triangulation, secured by posts. Six of the primary stations have been marked by stone monuments. The area covered by the triangulation exceeds 40 square miles; 96 angles were observed, usually by six repetitions direct and six reversed, sometimes by more frequent repetition. Assistant Gerdes and party have also carried on their office-work— computation of results—during the season. Secondary triangulation of keys and reef-This part of the work was conducted by assistant J. E. Hilgard from December 20, 1850, to February 1, 1851, and from that time up to June 3d, (when the season was at an end) by assistant L. F. Pourtales. The field of operations embraced Boca Chica, Key West, and the Marquesas, during the former portion of the season; and during the latter, Key Biscayne bay, including Soldier key, Ragged keys, Elliott's key, and Rubicon Point, with the main land from Shoal Point (twenty-five and a half miles, by the shoreline, southward from the mouth of the Miami river) to Turkey Point. (See sketches F No. 1 and F No. 2.) Mr. Hilgard gives the following statistics of his work: 9 stations occupied; 18 ditto observed upon; 100 angles, each the mean of six repetitions, observed (with the eight-inch Gambey theodolite, C. S. No. 24;) area of the work, 78 square miles. Mr. Pourtales reports 3 stations occupied; 18 points observed upon; 497 sets of measures of angles made; area of work, 70 square miles. His comparatively small progress is accounted for by difficulties occasioned by the prevailing trade-winds, and by the uncertainty often arising from lateral refraction—the lines passing over shoal water, which rendered it necessary to repeat the observations frequently. Much time has been occupied and great difficulties encountered, necessarily, in the erection of signals. Where it is necessary to insert them in the rock of the reefs the patent screw-pile of Mitchell has not yet been successfully applied; but it is hoped i. before the next season for observation, the object will have been accomplished by the addition of a heavy capstan-head applied to the screw-pile, and a tripod to steady it. Should this apparatus not prove effective, the object may be attained, as suggested by Mr. Pourtales, by a modified application of an arrange

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