Thanks to progress, cement is quickly replacing mud as the building material of choice in Eastern deserts. Big mistake, according to architecture historian Jean-Louis Bourgeois, who contends that not only is mud cheaper, it’s cooler and lasts longer. Not to mention the overwhelming aesthetic benefits: desert dwellings constructed largely of treated, unbaked, sun-dried mud become live-in sculptures, as in the case of this West African village of mud castles. This photograph is one of many by Carollee Pelos in the Field Museum exhibition “Spectacular Vernacular: Traditional Desert Architecture From West Africa and Southwest Asia,” on view July 22 through September 7. Admission to the museum, Roosevelt Road at Lake Shore Drive, is $2, $1 for kids 6-17, $4 for families; hours are 9 to 5 daily. Call 922-9410 for more.