from a dispatch received at this Department on the 23rd instant from Leonard Pierce, jr., United States consul at Matamoros, Mexico.

I have the honor to be, sir, your obedient servant,

WILLIAM H. SEWARD.

[Inclosure.]

CONSULATE OF THE UNITED STATES OF AMERICA, Matamoros, March 1, 1862.

Hon. W. H. SEWARD,

Secretary of State, Washington, D. C.:

SIR: * * * It has been with the greatest difficulty that I have established myself here, as the Confederate had used every possible exertion to get me driven out, and succeeded so far that none of the authorities, with the exception of the commanding general, would acknowledge my right until after the receipt of my exequatur. When I say the Confederate, I mean the military; most of the citizens of Brownsville being really Union men. The prefect (Martin Lougona, who was among the slain in the final assault), a man unknown to me personally, endeavored in every possible,manner to show his authority, and went so far as to enter room with ten armed men to search (as he said) for gunpowder. Although he would not acknowledge my right as consul until the arrival of my exequatur, still he had seen my passport and appointment, and knew that the general-in-chief had recognized me and had also given me permission to hoist my flag,which was flying over my house at the time.

The Confederate occupy both the Texan and Mexican side of the Rio Grande at its mouth, and use every exertion to prevent me from communicating with the U. S.ship Portsmouth.

The general commanding here, with most of his officers, are much against the people of the South, and, in fact, are all the better class of Mexicans. The general has said to me that he will endeavor to protect his side of the river, in which case I can then communicate freely. There are now in port fourteen vessels, among them one American only, from New York. As the only lighters here bear the rebel flag, they were unable to unload them while the ship of war may lay there, but the merchants have now purchased three steamboats and put them under the Mexican flag. The difficulty is obviated.

Matamoros is now the great thoroughfare to the Southern States. They pas their coffee, flout, and in fact all the supplies they receive through here. They have also a large pile of cotton on the east bank of the river, to take out when an opportunity offers, or, as they say, burn,in case of in invasion.

There are at Brownsville and Brazos Santiago about 1,200 men, among them some German companies, whose loyalty to the Southern Confederacy is much doubted in Texans.

* * * * * *

There are many of the citizens of Texans leaving since the Governor's proclamation calling out the militia, and some that have been prisoners and escaped;nearly all without friends or means to take them North.

I am, sir, very respectfully, your most obedient,

L. PIERCE, JR.,

Consul.