Rock miner Martin Marietta Materials (NYSE:MLM) was one of Wall Street's few winners yesterday. Its shares swam upward by about half a percent through the sea of red equity ink on a pretty bad day for the market. The reason: The company posted some pretty stellar results on a couple of fronts (less so on others).

First up: revenues. In 2004, those grew by 5% over the company's 2003 numbers. Next: earnings. Under generally accepted accounting principles (GAAP), operating earnings grew 16%, net earnings by 38%, and net earnings per diluted share by 39%, moving up to $2.66 per diluted share.

Where the good news stopped was on the company's cash flow statement, where free cash flow generation seems to have fallen off year over year. For 2003, Martin Marietta posted free cash flow of $157 million; for 2004, that declined to $103 million. Of course, things could be worse. Last month, rival Lafarge North America (NYSE:LAF) hit the rocks as its $216 million in positive 2003 free cash flow actually turned negative in 2004, in spite of a 5% increase in GAAP net income.

The exceptions to the rule in this industry were two: First, Florida Rock (NYSE:FRK), which eked out an infinitesimal year-on-year increase of less than 1% in its free cash flow. And Vulcan Materials (NYSE:VMC), whose free cash flow of $325 million in 2003 rose to $377 million in 2004. That 16% rise didn't quite live up to the 46% increase in Vulcan's GAAP net profits, however. This just goes to show that, when investors see GAAP profits being posted by companies in this industry, they shouldn't necessarily take free cash flow for granite.

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Fool contributor Rich Smith doesn't have a position in any company mentioned in this article. The Fool has a rock-solid disclosure policy .