Sophy Burnham, a self-tagged Maryland blue blood, has tossed together some highly disparate phenomena--from the persistence of fox hunting to the growth of agribusiness--to demonstrate that landed wealth is more prevalent, more enduring, and more powerful than we think. Also, latterly, more wounding--this apropos of another element, the rigors of growing up rich. But what her tour of landed estates turns up--after pages of spot claims--is no pattern of secure family ownership but a crazyquilt of keeping up appearances (Virginia), decay and dismemberment (the Hudson River Valley), enlightened management (Illinois' ""Scully Prairie""), corporate exploitation (the former Tevis Empire), and a businesslike barony (the King Ranch). She's left herself an out, however, by including among her ""landed gentry"" families that bought land--""a ranch, an island, a wailed retreat""--with fortunes made in manufacturing or commerce. Folks like the Astors and Rockefellers, for instance (though the former had the poor judgment to abandon Rhinebeck, N.Y., to real estate development). People of property, in other words, from which they derive incomes, as against those who are just well paid. These Burnham sees as constituting a social class, ""my class,"" about which she has some incontestable, some interesting, and some silly things to say. A reader might reasonably be struck by the narrowness and rigidity of her finishing-school days at Foxcroft and, at the same time, recoil from an effusion like: ""The cruelty of class. Dear God! You can't imagine how it tears a man to shreds."" All these slices of propertied life add up to a pop sociology stew but Burnham, not incidentally, is the author of The Art Crowd (1973), and this is another tattletale attention-getter.