What is the process that darwin described as "descent with modification?

The process that Darwin described as "descent with modification" is the process of evolution.

"Descent with modification" is one of the fundamental ideas behind Darwin's theory of evolution. According to Darwin, the characteristics of an organism are inherited. Offspring with inherited characteristics which allows them to compete best with the limited resources in the environment will survive. Organisms will pass the traits providing an advantage to survive and reproduce to the next generations. Over time and generations, the traits providing reproductive advantage will become common among the polpulation. This will lead to change in populations over generations in a process called the "descent with modification".

it is a learned trait

explanation:

answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.