Read it through once

Attempts have often been made to calculate the rate of growth of such peat-mosses. A great many of them began to develop on the mud left by the ice-sheet when the glaciers retreated at the end of the Ice Age. Those mosses are therefore probably 200,000 years old. Some of our Scotch mosses are twenty to twenty-five feet in depth, which gives a foot in 10,000 years. By calculation of the weight of the peat formed, Aigner made out that a certain moss was 20,600 years old, and was growing at the rate of two inches in a century.