Profitability of small- and medium-sized enterprises in Marshall’s time: sector and spatial heterogeneity in the nineteenth century

New data on profit heterogeneity of small- and medium-sized firms for 1861–81 in England and Wales are used to reinterpret Marshall's contemporary insights. Profit level differences are chiefly explained by location, mainly urbanisation effects. But profitability (profit per worker) is mainly explained by sectors, at both 1-digit and 5-digit level. Sector market opportunities reflected barriers to market entry which limited substitutability for the services of the professions, some manufacturing and maker-dealing industries. Localisation mainly reflected urban/rural differences, accessibility to railways and to a lesser extent waterways. Differences in firm-level organisation (measured by portfolio diversification and partnerships) were less significant for explaining profit heterogeneity than sector or localisation. Demographic effects such as an entrepreneur's age had little significance. Marshall's insight of convergence to mean industry-sector profitability, with localisation as a secondary influence, is confirmed, but there remain unexplained elements of heterogeneity indicating important roles of entrepreneurial agency.