Last week, Wall Street couldn't think about anything other than the specter of Fed tapering. This week, it's found a new central bank to disapprove of. China's central bank, opting not to interfere to drive money market rates lower, is being fingered as the villain behind today's drop, which took more than 6% off China's most prominent equities index on Monday. The S&P 500 Index (SNPINDEX:^GSPC) lost 19 points, or 1.2%, ending at 1,573, a nine-week low. As you can imagine, its three biggest laggards all sold off ruthlessly. 

The largest decliner was the pharmaceutical company Allergan (NYSE: AGN), which slumped 11.6% after the U.S. Food and Drug Administration proposed less stringent requirements for companies applying to market generic versions of an Allergan product. This column cited rumors of emerging generic competition for Allergan's Restasis eye drop as a reason for the stock's 3.7% drop on Friday. While today's FDA release doesn't leave the door wide open for generics, it makes the path to approval far less daunting. 

Iron ore and coal producer Cliffs Natural Resources (NYSE:CLF) shed 7.6%, continuing a dismal 2013, in which investors have seen shares lose nearly 60% of their value. The stock reached a new 52-week low today, as demand for coal as an energy solution continues to ebb. The basic materials sector was also the worst-performing area in the markets on Monday. Considering the fact that Cliffs shares are more than twice as volatile as the market itself, today's losses aren't too befuddling. 

A major reason that basic materials companies weren't up to par today stems from the concerns coming out of China. Not only are interest rates on the rise, but Goldman Sachs lowered its estimates on the country's growth today. China, as a major energy consumer, holds huge sway over companies like Peabody Energy (OTC:BTU) that not only mine and market coal but act as brokerages for the resource as well. Accordingly, Peabody shares fell 7.2% on Monday.