Hey Pete,
Alot of the traditional pocket knife style came about as a particular job required a distinct type of blade. In other words, the knife sometimes evolved into a form to meet certain needs of the user. A very typical example would be the stockman pattern.
The stockman evolved from the cattle knife of the 1860's-70's. This was a cowboys working tool. The clip blade was an all around cutting tool, for everything to slicing bacon, opening a feed sak, to skinning small game. The spey blade was used to make a bull into a steer. At roundup when this was done alot, you got to have mountain oysters for dinner. Oh yum!
The sheepsfoot blade was a hard use blade, to spare the main clip. The cattle knife evolved into the premium stockman about the 1880's.
The trapper pattern came about when muskrat and racoon coats came into vogue. With smaller game to skin than the large western buffalo and beaver, a smaller lighter knife was needed. The trapper came into its heyday about the late 1890's to the early 1900's. It remained very popular for a very long time through the WW2 era. Along with the evolution of the trapper came the close spin-off, the muskrat.
The barlow has roots so far back there has been conflicting accounts. Some give credit to a cutler named Barlow, but there was an exellent article in Knifeworld about 10 years ago, where they had dug up samples of clasp knives from a wreck at the bottom of the Thames river from the late 1600's that had the long bolster that was a barlow trade mark. I imagine that some cutler long ago discovered the longer iron bolster gave more strengh to an otherwise cheap folding knife and it became a widespread thing to do. The long bolster can be seen on samples of European penny knives of the late 1600 and 1700 period.
The European penny knife gave birth to a couple of designs that are still around to this day. The sodbuster is one of them. This design seemed to evolve in the German part of northern Europe around the 1700-1800s as a form of the simple clasp knife. It was a cutting tool of farm laborers and such. One can only imagine that durring the large influx of immigrants to America in the 1800's from Europe, alot of these type of knives made thier way here in the pockets of German, Dutch, and Polish homesteaders looking for a better life. A simple blade with cheap iron liners, with a couple of wood or horn scales rivited on ment a low cost knife for a farmer wanting to cut a length of twine to bind up the sheaf of whatever he had cut down. In most of the museums I've visited this seems to be the most popular pattern of pocket knife. In the civil war museums around Maryland and Virginia, in the displays of soldiers effect found on the battlefields the simple single blade folder is very plentifull. Out west I've been to the fur traders museum in Nebraska, and one in Colorado and that type of knife seems as popular in the 1820 to 1850 period as the barlow became in the 1850 to 1880 period. It seems that after 1880 there appeared more diverse styles of folding knives.
If you can get a hold of the book "American Knives" by Harold Peterson, published by Charles Scribner's Sons, New York, 1958, its got a whole chapter on the evolution of the pocket knife in America. The Library of Congress card number is 58-7523.
