|"One Tree Hill, Auckland"|
Print of a sketch by NZ artist Peter Arnold
Confusingly these prints were sold both as black and white images and hand coloured (by the publisher, not the artist). Either coloured or uncoloured they are reproduction prints, not original (i.e. handmade - for example an etching) prints or sketches. Their value is decorative rather than investment, nicely framed they are worth around $NZ50 each.
An example of the artists' style is the print of Auckland's One Tree Hill illustrated here - there were at least a couple of dozen scenes published in this technique and of similar appearance.
If you are still convinced that you may have an original sketch rather than a reproduction we'd recommend getting an expert in paintings and drawings to take a look at the artwork in real life, try contacting an auctioneer of fine art near you or your local city council run art gallery.