This picture shows a different spelling than the Purbeck of Dorset, England but John C Ash and his brother Edmund and their parents would no doubt have a good knowledge of the type of clay that made it famous, at least for Josiah Wedgewood, called ball clay discussed in the following article.
I have no proof but if the land they homesteaded on bears any resemblance to Saskatchewan's gumbo clay then it makes perfect sense.
The main concentration of ball clay in Dorset is to the north of the Purbeck Hills centred around Norden. Ball clays are sedimentary in origin.Large quantities were ordered by Josiah Wedgwood from 1771 and this led to the construction of Dorset's first railway in 1806. This was the Middlebere Plateway, which connected clay workings owned by the London Merchant Benjamin Fayle in the Corfe Castle area, to a wharf on Middlebere Creek in Poole Harbour. Other similar tramways followed, including the Furzebrook Railway (c.1840), the Newton Tramway (1854), and Fayle's Tramway (1907). With the coming of the London and South Western Railway line from Wareham to Swanage in 1885.
The Ash farm at Perbeck, Alberta, Canada.