This cabinet card of a young child and a dog is an intriguing one, not only because of the anonymity of the subject. It appears to have been taken in an unknown rural location - on a fairly smooth, but stony track with a rough stone wall and a hillside in the background - but the studio location is in Bramble Street, Derby.
I have never come across any reference to the The Portland Photo Co. previously - that's why you'll currently find no entry for it in my Index to Derbyshire Photographers & Studios. From the style of the card mount and the clothing worn by the child, I would venture a guess that it was taken in the late 1890s or early 1900s, say between 1895 and 1905.
The only photographer that I know of who worked in Bramble Street, Derby during this period was Frank Birch, who was probably there from late 1894 until c.1898, after which he removed to premises located at Nag's Head Yard, 64 St Peter's Street. It was during this period that the cabinet card presented in a previous article about Frank Birch was produced. Then, in 1903, Birch became manager of the Derby Stereoscopic Company, located at 36 Victoria Street.
I wonder if Frank Birch also traded for a short while as The Portland Photo Company? There was, and still is, a Portland Street in Derby, but this is situated some distance away in the suburb of Litchurch.