Caterpillar

Heavy equipment maker Caterpillar plunged 6 percent Thursday after lowering its revenue forecast and announcing a restructuring.

Joy Global, a maker of mining equipment, slipped 1 percent. Falling prices for copper and other basic materials have hurt those companies.

The Dow Jones industrial average lost 78 points, or 0.5 percent, to 16,201. It had been down 263 points earlier.

KEEPING SCORE: The Standard & Poor's 500 index fell 18 points, or 1 percent, to 1,919 as of 10:15 a.m. Eastern time. The Dow Jones industrial average dropped 188 points, or 1.2 percent, to 16,083. The Nasdaq composite fell 49 points, or 1.1 percent, to 4,702.

Caterpillar and 3M released weaker-than-expected earnings, pulling indexes lower Thursday.

Some companies bucked the downward trend. General Motors, Southwest Airlines and Raytheon all rose after announcing stronger results than analysts anticipated.

The Dow Jones industrial average lost 119 points, or 0.7 percent, to close at 17,731.