The brittle behavior aspects of the undrained shear strength of a varved clay deposited in a glacial-era lake are presented. The cause of the brittle behavior is surmised to be calcareous in nature. The calcareous material is an integral part of the natural soil structure. The influences of rate of strain, relative level of consolidation stress during shear in comparison with the consolidation stress, specimen quality, and mode of loading are illustrated by diagrams of shear strength versus mean effective stress (q-p) paths. The undrained shear strength to consolidation stress (c/p) ratio varies systematically. The brittle behavior is less prominent during laboratory shear strength testing, when the soil's natural structure is disturbed. The correlation of laboratory-measured undrained shear strength with field-measured vane shear strength values is presented.