Dig until you find stable soil
When engineers have to build over soft, sandy ground, they often dig deep into the earth until they reach soil that's capable of supporting the structure's enormous weight. So you recommend that the builders pour reinforced concrete piles into the earth and build the cathedral on top of them. This way, the heavy weight of the cathedral is distributed through each of the deep piles to the stable ground below.
All 384 million pounds of the John Hancock Center in Chicago rests on piles that extend down to bedrock. Some piles extend 191 feet below the surface of the earth! You've made the right choice. Congratulations!