Logan's Line, also known as Logan's Fault, is an important geological feature in eastern Canada. It is reasonably well known, especially in the Quebec City area, but most people would be hard pressed to explain what it is.
Logan's Line marks the boundary between two geological provinces. These are the relatively undisturbed and mostly flat lying sedimentary rocks of Early Paleozoic age of the St. Lawrence Lowlands to the north or west of Logan's Line, and the overturned, folded and thrust-faulted rocks of the Appalachian mountain belt south or east of Logan's Line. The Appalachian rocks are the roots of an ancient mountain system that ran from Newfoundland in the north to Louisiana in the south.
During his fieldwork near Quebec City in 1860, William Logan became the first person to identify this feature and to recognize its significance. He surmised correctly that it was a fault, although he did not know the extent of the mountain belt that it defines. Logan's Line follows roughly the mouth of the St. Lawrence River then passes between Anticosti Island and the Gaspe Peninsula.
Category: Science Advances
Logan, W.E., Murray, A., Hunt, T.S., and Billings, E., 1863. Geology of Canada. Report of Progress from its Commencement to 1863; Geological Survey of Canada, 983 p. [accompanied by an Atlas of Maps and Sections.] doi:10.4095/123563
Alcock, F.J., 1945. Logan's Fault; Journal of the Royal Astronomical Society of Canada, v. 39, p. 213-216. https://adsabs.harvard.edu/full/1945JRASC..39..213A