 Under the pressure of a "joint account" set up by Ryan and Rockefeller of nearly a million and a half shares of Anaconda Copper Company, prices fluctuated from $40 in December 1928, to $128 in March 1929.Selling large volumes of shares rather quickly causes the bottom to fall out of the market; investors lose confidence and dump their shares, causing a domino effect.Small investors would purchase blocks of shares on credit, and when they could not sell at or above the given price, had to sell the shares at a loss when the banks called on their loans for the purchase of said shares.