Dr. jekyll needed which of these ingredients to make another batch of his potion?

The ingredient that Dr. Jekyll thought that he needed is salt to make another batch of his potion. However, he found out later that it was not this ingredient but the impurity in it that was the vital chemical in his potion.

weathering - colorado river carves land in arizona to form the grand canyon. cracks form in a sandstone wall surrounding a house. a marble statue near the science museum is changing color due to rainfall

erosion - after a rainstorm, soil and rock piees litter the roadways. the sand dunes in the sahara desert are changing shape.

here's your answer.