The S&P has made an all-time high for nine-straight quarters and the index only continued to climb Tuesday, leading some market observers to warn a bubble looms, but CNBC's Jim Cramer says the gains appear sustainable.
To make his point, Cramer noted that Caterpillar, Merck and Microsoft were the best performing stocks in the Dow Jones industrial average in the first quarter, which ended Monday. Forest Laboratories and Green Mountain Coffee Roasters were the S&P's best gainers in Q1.
"When you look at these stocks, you know what these stocks are? Stocks that have been around," Cramer said on "Squawk on the Street." "This is not cloud. This is not software as a service."
Undoubtedly, cloud computing has been one of the hottest sectors on Wall Street lately. Over the past few weeks, a slew of cloud computing companies made initial public offerings, seeing their shares soar. Biotechnology stocks have also enjoyed considerable gains, with the sector gaining 51 percent last year and 13 percent in 2014. However, the strong performance in both industries has led some market observers to argue the gains may be too fast, too soon.
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"If you look at the makeup of the last quarter, it was not the stocks that we thought that were bubblicious," Cramer said. "It was Caterpillar."
S&P and Nasdaq have produced five consecutive quarterly gains for the first time since 2007. The Dow, however, ended Q1 down 0.7 percent.
"How many quarters can we have 'It's a bubble' before we have to declare it's not a bubble?" Cramer asked. "Can we just stipulate there's something going on here—that is not bubble?"