Interpreting the Collections

The Raw Materials of Science: Field Notebooks

Sketch of sedimentary rock strata from William Logan's notebook
Source

Because field notebooks contain the most complete record of locations visited and observations made, they continue to be consulted by geologists many years after the original work was done. The Logan notebooks are a similarly rich source for historians, but they can be difficult to read due to his practice of taking notes initially in pencil and later writing over them in ink. Logan used his field notebooks to record travelling expenses, interviews with local people and their suggestions, but above all these pages are devoted to the heart of surveying: geological observations and sections.

William Logan's rock hammer
Source

The point of a nineteenth-century geological survey was to determine what kind of rocks underlay a given region and thus be able to predict its economic potential. Exposures of bedrock can be very limited, however, apart from eroded surfaces along coasts and rivers, so the problem was to infer the structure of an entire region from observations made in just a few places. This is possible in well-stratified areas because the same strata (layers) can be traced from point to point and recognized by their rock type, minerals, and fossil contents. Since the strata are almost always tilted to some extent, the rocks exposed at one location will lie below or above those at another, meaning that they are geologically older or younger. Hence, a geological surveyor had to record not only the colour, type (e.g., sandstone, limestone, shale), and any special qualities of each layer, but also its thickness, the compass direction in which it dipped, and its angle of inclination.

Map and sketches from Logan's notebook
Source

At any given outcrop (exposure), the surveyor would construct a geological "section" by listing each layer in order, along with the data noted above. Thicknesses were measured directly or, for larger units, by pacing along the ground and calculating the value mathematically according to the dip angle. Combined with an accurate topographical survey of an area -- which the geologists usually had to do themselves -- these sections made it possible to assign each piece of territory to a specific geological formation, and thus to colour in the geological map.

Among the notebooks selected for the Written in Stone digital collection are those corresponding to the field seasons covered in Logan's 1843-1846 journals, allowing a direct comparison of his personal experience and his scientific work in these crucial early years. While the journals have a strong subjective authorial presence, the notebooks are much more dispassionate, objective, and are generally written in the passive voice. There are also notebooks covering his 1842 visit to Canada after his appointment to the Geological Survey of Canada, and his work in Nova Scotia and New Brunswick before he reached Gaspé in 1843; atypically, this last item contains some pages of personal journal entries as well.