This work investigates the petrogenesis and structural classification of granitic and migmatitic rock formations found within the Fennoscandian Shield. J.J. Sederholm, a pioneering figure in Precambrian geology, utilizes extensive field observations and microscopic analysis to argue for the complex metamorphic origins of migmatites. He establishes a framework for understanding the interaction between intrusive magmas and pre-existing crustal rocks.

Geologists and historians of science recognize this text as a foundational contribution to the study of metamorphic petrology. Readers frequently note the technical density of the prose and the historical significance of Sederholm's observations in defining the nature of migmatites.