The ore was first extracted through surface diggings, but these were quickly exhausted and miners had to tunnel underground to reach ore bodies. Unlike most silver ore deposits, which occur in long thin veins, those of the Comstock Lode occurred in discrete masses often hundreds of feet thick. Sometimes, the ore was so soft it could be removed by shovel. Although this allowed the ore to be easily excavated, the weakness of the surrounding rock resulted in frequent and deadly cave-ins. The excavations were carried to depths of more than 3,200 feet (1,000 m) (eventually, after years of work).