Sentence:  Here and there are beds of <WSD>oolites</WSD>, for example, made of little rounded grains – like millet seed – that form only in agitated warm waters, such as you might find off the Bahamas today. 
Meaning of the word marked with <WSD> tags:  A rock consisting of spherical grains within a mineral cortex accreted around a nucleus, often of quartz grains.