The M3 "broad" money supply, watched as an early warning signal for the economy a year or so later, has been falling at a 5pc annual rate.
Similar concerns have been raised by David Rosenberg, chief strategist at Gluskin Sheff, who said that over the four weeks up to August 24, bank credit shrank at an "epic" 9pc annual pace, the M2 money supply shrank at 12.2pc and M1 shrank at 6.5pc.
"For the first time in the post-WW2 [Second World War] era, we have deflation in credit, wages and rents and, from our lens, this is a toxic brew," he said.
It is unclear why the US Federal Reserve has allowed this to occur.
Chairman Ben Bernanke is an expert on the "credit channel" causes of depressions and has given eloquent speeches about the risks of deflation in the past.
He is not a monetary economist, however, and there are indications that the Fed has had to pare back its policy of quantitative easing (buying bonds) in order to reassure China and other foreign creditors that the US is not trying to devalue its debts by stealth monetisation.
Mr Congdon said a key reason for credit contraction is pressure on banks to raise their capital ratios. While this is well-advised in boom times, it makes matters worse in a downturn.