20 DISCUSSION ON THE ORIGIN OF THE TRIAS, 
Mr. R. D. Oldham asked " What is a desert ? " He referred 
to sand deserts, rock deserts, and mud deserts, the last having a 
slightly rolling uneven surface in which rains accumulate. He 
considers that the only agency capable of forming pure sands 
of large extent — hundreds of miles — and very thick, is wind. 
Mr. Clement Reid discussed the peculiar plant adaptations 
found in deserts. They are generally provided with stiff stems 
and fronds like Cycads. As far as we know the Triassic flora, 
the same habit occurs. 
Dr. J. J. H. Teall pointed out that 25 years ago, Sir A. 
Ramsay, speaking at a meeting of the British Association at 
York, suggested that the British Trias was of desert origin. 
