To expand a little on what williamlayton said, there is an exhibit at the Texas Ranger Museum in Waco that has an actual horse that has been taxidermistized. It has the accoutrements of an early (post-Mexican war but pre-Civil war) Texas Ranger (saddle, canteen, blanket, etc.) and attached on each side of the front of the saddle are holsters for a brace of Colt Walker revolvers. (I've always thought those Walkers were too heavy for belt holster wear ala Gus in Lonesome Dove.) The museum is a great place to visit if you are interested in guns and/or the Texas Rangers.
Listed below are excerpts from some books that indicate packing two handguns wasnt really uncommon.
Wild Bill Hickok seldom or never used holsters. He usually carried two pistols in his waistband, their butts pointing inward for a cross-arm draw.
(Dallas) Stoudenmire never wore revolver-holsters. He had been presented with two fine silver-plated Colts, caliber .45, by Beneky and Pierce, pioneer hardware men. These he carried in leather-lined hip pockets. He maintained always that he could draw more quickly from his pockets than from holsters.
In Evergreen, the tiny community flanking the Austin-Brenham road, Bill Longly was a leading spirit among the younger generation. His size, his courage, his amazing skill with twin Colts, a certain fierce élan which was never to desert him, made him a marked figure among gatherings at the crossroads blacksmith shop and store, under the wide shade of the court house oakwhich had served both as justice court and gallows, in its day, ant which still stands a brooding giant over that quiet land.
The oldtimers who knew him well used to marvel in my hearing over his skill. They said that his hands, snapping to the butts of the .45s in their cut-down holsters, were like racing snakes streaking into holes. He was a deadly shot with either handwhich was not so usual with gunmen who pulled as flashingly as he. Frequently, the man who was extra-quick on the draw figured to make up, by the number of shots he fired, for any lack of accuracy in aim. But not Long-Haired Jim Courtright!
All of the above are excerpted from Eugene Cunninghams Triggernometry.
In the spring of 1871 I had my first trip to the frontier of Texas.
Those big, fine frontiersmen, each wearing a pair of revolvers and most of them carrying a Winchester,
He was heavily armed, wearing two six-shooters and carrying a Winchester in front of him.
These last two are from James B. Gillettes Six Years with the Texas Rangers 1875 - 1881.