Sentence:  Seating himselfe within a darkesome cave, / (Such places <WSD>heavy</WSD> Saturnists doe crave,) / Where yet the gladsome day was never seene ... 
Meaning of the word marked with <WSD> tags:  Laden with that which is weighty; encumbered; burdened; bowed down, either with an actual burden, or with grief, pain, disappointment, etc.