Christopher Lloyd and Joachim Pissarro have kindly confirmed the authenticity of this work.
The technique of this drawing is outstanding in its use of hatching, cross-hatching and in the incorporation of parts of the paper left blank as part of the composition. This intricate 'knitting' of textures - which Pissarro himslef called 'tricotage' (knitting) - finds expression in his oils of the late 1870s-early 1880s; the motif itself is a development of the magisterial paintings done at L'Hermitage at the end of the 1860s.
Pissarro continued to use the same compositional principles in the late 1870s, but experimented more with his technique. It is this last aspect that this drawing masterly exemplifies.