Imágenes de páginas

out to completion, so that partial benefits shall be realized in proportion to its progress. The commerce of Mobile bay, and of the harbors of Cat and Ship islands, has great need of such facilities for navigation. (See Appendix, Nos. 35 and 36.)

For the determination of differences of longitude by methods described in my last annual report, I have had in view the establishment of a station for telegraphic connexion between New Orleans and Washington, by the line of the coast or by a line passing through Cincinnati and the valley of the Mississippi. Assistant Gilbert recommends Fort Wood or Fort Pike as suitable and convenient points for the purpose of connecting with the coast line of telegraph, being included in the scheme of triangulation, and within a few hundred yards of the telegraphic wires from New Orleans to Mobile.

Triangulation, (sketch H.)—This portion of the work was under charge of assistant Samuel A. Gilbert, who was supplied with a small vessel for transportation, and was aided, during the latter part of the season, by Mr. Charles M. Bache. The party was engaged for five months, ending May 20th—first, in the triangulation of Biloxi bay; second, in connecting that series with the main scheme to the eastward; third, in the repetition of observations of the previous year in St. Louis bay, unsatisfactory through defect of the instrument; and finally, in the extension of the secondary triangulation westward over Mississippi sound and Lake Borgne to the eastern shores of Lake Pontchartrain. Mr. Gilbert's summary of results is as follows:

« The area covered by the triangulation of Biloxi bay is 48 square miles. The area covered by the work necessary to the connexion with the main series, and previously covered by it, is 40 square miles. The area covered by the triangles remeasured is 96 square miles—being in all 184 square miles.

“The area covered by the triangulation as yet unobserved, but of which all the signals have been erected, is 608 square miles. The number of angles measured is 67, for the determination of which 94 series of 12 repetitions each, and 8 of 6 repetitions each, or 1,176 angles, were observed.”

The experience of the party indicates the months of May and June as more favorable for observing, in this region, than the three months preceding.

Assistant F. H. Gerdes made a brief visit to this section, which was employed in erecting permanent marks at the main stations.

Topography, (sketch H.)—Assistant W. E. Greenwell was engaged in this duty, aided by Mr. W. M. Johnson, and having the use of the Coast Survey schooner Phoenix. The resulting work is indicated by the accompanying sketch, which embraces (in three sheets, marked 18, 19, and 17, respectively) Pass Christian and its vicinity, the Bay of Biloxi, and coast eastward as far as West Pascagoula river. Upon the general topography of these sections, Mr. Greenwell's remarks may be quoted as interesting:

“The character of the country embraced in sheet No. 17, or the one running from West Pascagoula river to Biloxi bay, is similar in every respect to that described in previous reports—the shores being low and smooth, thickly wooded to the very water with pine, principally, interspersed with magnolia and hammocks of live-oak. Skirting the shore along is here and there a settlement, with small spots of cultivated ground, whilst the interior, for miles and miles back, is but a dense forest of pine, apparently in its wild and primitive state.

“ The character of the topography upon sheet No. 18 is very similar to the one just described. The town of Pass Christian, situated upon a ridge of fast land, about twenty feet above high water, sloping gradually towards the sound and again back in the interior, presents the only feature different from sheet 17. Around it is the same wild, thick forest of pine as seen along the whole coast.

“The features of the country embraced in the Biloxi sheet are somewhat different from that just described. On the east shore of Biloxi bay the banks are abrupt, being from twenty-five to thirty feet in height, and of a red clayish soil. Here, too, unlike the other parts of the coast, the shores are quite thickly settled, and improvements have been made, and are still making, which, in a few years, will make it a place of some importance.

Along the shores of the “Back bay,' and on the banks of the bayous emptying into it, are at present, in successful operation, many mills, foundries, &c. From these and other resources a trade between Biloxi and New Orleans is kept up, amounting to about $390,000 per annum, keeping in constant employment about eighty or ninety vessels, amounting in all to about three thousand five hundred tons."

During the season of five months (December to June) the area surveyed was 65 square miles; the length of shore-line 227, of roads 27, and of streets and wharves 15 miles.

Hydrography, (sketch H, Nos. 7 to 10.)— The party under charge of Lieutenant Commanding James Alden, United States navy, assistant in the coast survey, was engaged in the survey of Bon Secours bay until its completion, when that officer was transferred to another section. The operations were conducted during the remainder and greater portion of the season by Lieutenant Commanding B. F. Sands, United States navy, assistant in the coast survey. The steamer Walker was appropriated for the use of this party.

The work off the entrance of Mobile bay was extended off-shore, both eastward and westward, (south of Dauphin and Petit Bois islands,) to the distance of eight or ten miles. Pass Christian, in Mississippi sound, was, in compliance with a special request of the residents, closely sounded from Henderson's Point to near Pitcher Point, and three and a half miles from shore. It is thus described by Lieutenant Commanding Sands:

"A depth of seven feet can be brought into the channel from the west by keeping the west beacons open to the southward, passing to the southward of the first beacon and northward of the second. At the eastern beacons it is rather shoaler; 6.3 feet can be taken in, with the inner beacon open to the eastward of the new church steeple until nearly up with that beacon, and thence to the steamboat wharf. The bottom being soft and the current strong, I should suppose a mud-machine could, at comparatively little expense, deepen the channel at the east and west beacons sufficiently for steamboat navigation.”

A reconnaissance was also made, by the same officer, of the Missis

sippi delta, to which I have already referred as showing considerable change. “The inarshes have made out seaward, mud-lumps have been washed away, and others formed.” From his report I quote the following useful advice for entering the Mississippi river:

“On account of the frequent changes on the bars, no sure sailingdirections can be given for crossing at any of the passes. Vessels should not approach the shore nearer than the depth of ten fathoms without a pilot, as it shoals up from that depth rapidly; and at night, after seeing the light at Northeast Pass, they should heave to or anchor outside of ten fathoms until daylight, when the pilots and tow-boats come out.

"The tow-boats generally anchor inside of the entrance, and in fair weather cruise off from ten to fifteen miles. Vessels are rarely delayed for want of tow-boats, as there is considerable competition, and they keep a good lookout for the offing."

The progress effected this season is shown in sketch H, of which the sheet marked No. 11 indicates the work of Lieutenant Commanding Alden, the remaining sheets that of Lieutenant Commanding Sandsthe former embracing 95 square miles of area, 223 miles of soundings, and 13,760 casts of the lead; the latter, 275 square miles of area, 688 miles of soundings, and 28,244 casts of the lead. The time employed was from January 16 to June 10, 1851.

From the results furnished by the hydrographic surveys, sailingdirections for Horn Island pass were made out and communicated to parties interested. (See Appendix, No. 37, and sketch H, No. 7.)



The work in this section has been conducted on the scale of previous years, three parties being in the field. Its progress is represented on the general sketch I. The triangulation has been carried from the vicinity of Galveston as far westward as the Brazos river, and all the primary and secondary station-points secured by permanent marks. An attempt to extend the secondary work into East bay failed, from insufficient depth of water, no means of land transportation being accessible. The topography of the bays about Galveston has been completed, as also the hydrography of the harbor, entrance, and approaches. The chart of Galveston entrance is in course of reduction for publication, and its engraving is provided for. A hydrographic reconnaissance and delineation of Aransas Pass and minute examinations of sites for light-houses in Galveston bay will be reported under their proper head. The rapid and extensive changes of the Aransas bar will appear worthy of special notice.

Peculiar difficulties are opposed to the work by the climate and topography of this region, which disturb the atmosphere so as to destroy its transparency; and which have induced the recommendation by assistant Williams of a diminished length of sides for the triangles. The obstacle of the belts of timber on and about the Brazos, which proved somewhat in the way of the triangulation, is supposed to be the only feature of the kind on the coast of Texas, from the Sabine to the Rio Grande.

ides have been Chese tides are Mobile bay, in

Hourly observations of tides have been instituted, and will be kept up by observers stationed at Galveston. These tides are observed and discussed on the same plan as those of Cat island and Mobile bay, in 1848 and 1850–51, and as at present at Key West-forming part of a system for ascertaining the tidal phenomena of the Gulf of Mexico.

Triangulation, (see sketch I.) Assistant James S. Williams has been in charge of this portion of the work, aided by sub-assistant Spencer C. McCorkle, who was for the most part separately engaged in reconnaissance and observations for the secondary and tertiary triangulation. The Coast Survey schooner Belle was in the service of the party.

The main triangulation has been connected, from the newly occupied primary stations, Chocolate and Hall's bayou, with that of the previous season. In extending the scheme westward from the new station Peninsula, assistant Williams was encountered by the serious, and, on this coast, exceptional obstacle, of heavy belts of timber on the Brazos river, Oyster creek, and Bastrop bayou. He has, however, so selected the points Jupiter and Hamilton, that the line from the Peninsula to the former, although striking the villages of Velasco and Quintana, passes along a street, and the lines from Hamilton to the other two points pass through openings in the timber.

In observing over the long lines of sight of the main triangles, great obstacles are encountered, which Mr. Williams thus enumerates : « The climate of this region, unless the last season is an exception to its general character, is singularly unfavorable for extended geodetic operations. The stormy winter, the short twilight, and intense heat of cloudless summer; the frequent, almost constant, high winds; the hazy, mnisty air,--all battle against progress; indeed, the air may be said to be clear only during a norther, when it is impossible to make an instrument steady on its high tripod.”

In one case, twenty-three days were occupied in endeavoring to effect measurements that in a favorable atmosphere would have required but a few hours. Mr. Williams recommends contracting the sides of the main triangles, that more results may be obtained in proportion to the time.

The secondary and tertiary triangulation has substantially advanced as far as the Brazos river. The contraction of the side between Oyster creek and Rattlesnake secondary stations, somewhat marring the symmetry of the general scheme, was a judicious measure of economy to avoid cutting through heavy timber. Some time was lost in an unsuccessful attempt, before mentioned, to extend the work into East bay, in the other direction. A

In reference to the preservation of stations, assistant Williams reports: “ The primary points that have been occupied during the season are each marked by an earthenware cone, buried three and a half feet below the surface; upon this a wooden piece, one foot square, rests, and supports a granite block, two feet long and ten inches square, marked with a cross upon its middle point. Besides this, three smaller granite blocks are sunk to within three inches of their upper surface-north, south, and east from the centre, and three feet distant. The secondary points are marked by the cone in the centre, and the three blocks disposed, as above, around it.”

In this season, from December 10, 1850, to June 10, 1851, 8 stations have been occupied, of which 3 were primary, and 5 secondary; 58 angles measured from 2,484 observations; 15 signals have been put up, giving 163 square miles in area of primary, and 99 square miles of secondary triangles. The instrument used by assistant Williams was C. S. theodolite No. 31.

Assistant Williams, in his report of a reconnaissance for triangulation, remarks upon the unusual topography of a portion of the coast, as follows: “I have found along the Brazos river and Oyster creek (which run nearly parallel for twenty miles from the Gulf) belts of heavy timber, principally live-oak, coming down to within five miles of the gulf, and varying in breadth from one to three miles. Crossing Oyster creek at a point about fifteen miles from the gulf, and proceeding eastward, I found heavy live-oak timber on the head of Bastrop bayou."

Topography.The party of sub-assistant J. M. Wampler was in the field during the first five months of 1851, and had in use the Coast Survey schooner Nymph. Its duties were made arduous by an inclement season, and by the necessity of often working at stations covered with water.

The results of the work are comprised in a complete topographical map of Galveston bay, (see sketch I, No. 2,) of which about one-third had been accomplished the previous season. The amount of work may be reckoned as follows: shore-line surveyed, 281 miles; area of country, 1984 square miles; and 25 miles of roads. It includes West bay, East bay, and Bolivar peninsula, Turtle bay, and the delta of Trinity river.

Hydrography.Lieutenant Commanding T. A. Craven, United States navy, assistant in the coast survey, was in charge of the party, and of the Coast Survey schooner Morris, engaged in this work. He has made a survey (see sketch I, No. 2) of Galveston harbor and its approaches. Sheet No. 1 comprises the harbor, and sheet No. 2 the bar and approaches.

During the season, from March 19 to June 29, the lines of soundings amounted to 484 miles; the number of soundings being 31,100, and the area surveyed 55 square miles. The soundings were made in depths of from one foot to eight fathoms. 1,665 observations of angles were made.

The depth of water on Galveston bar is stated to be twelve feet.

Lieutenant Commanding Craven has also made a special examination of Clopper's bar, Red Fish bar, and Half Moon shoal, in Galveston bay; and of Aransas Pass, the entrance used for Corpus Christi as well as Aransas bay. All of these (see sketches I No. 2, and I No. 3) will be referred to in their proper connexion. I may quote here, however, Lieutenant Craven's mention of the remarkable changes about Aransas Pass, (sketch I, No. 3,) as follows:

“The point in my reconnaissance designated as · Old Range,' was, in 1846, within 120 yards of the channel, and the Range' itself was awash. It is now 350 metres from the beach, and upwards of half a

« AnteriorContinuar »