“On the left is the foot of the mountain which I climbed y’day 3,500 feet above sea level.”
“George Hotel Penrith
Having lovely weather and I am feeling ever so much better in health. Are you keeping well. I don’t want you to get done up by staying at the works all day long. However I will be home on Tuesday & be able to make things easier for you. Can you manage if I don’t return until Tuesday afternoon[?]. EYP”
“The train from here does not get in to S’land until after dinner.”
Can that postmark really be Penrith 9pm 11th September 1915?
So Fred Crosby – possibly Martin’s father, worked in a tough job at the Works. Joblings the glass works was right across the road (where B&Q is now). Maybe he worked there? ‘Works’ is what it would have been called. ‘Yard’ would be a shipyard. So, not Pickersgills.
A CLUE.
THE GREAT FERN STREET POSTCARD MYSTERY 
Fred is James Frederick Crosby, Martin’s father. According to the 1911 census he was a foreman for a paint manufacturer – perhaps the fumes were getting to him. He was known in the family as Fred to distinguish him from his father, also James. The concern and tender tones suggest a female relative; not his wife (Ann), nor a daughter or daughter-in-law (none of his children were married in 1915), but perhaps his oldest sister Elizabeth Dolan or her daughter (also Elizabeth) – the last letter of her signature could be a D rather than a P – compare it with the tailed D in “Durham”
There may have been many paint manufacturers in Sunderland in the 1810s, but one – William Carter of Avon Street was within easy walking distance of Fern Street
https://maps.google.co.uk/maps?saddr=Avon+Street,+Sunderland&daddr=Fern+St,+Sunderland&hl=en&ll=54.906447,-1.382346&spn=0.01505,0.042272&sll=54.906819,-1.382832&sspn=0.01505,0.042272&geocode=FQnCRQMdIx_r_ykBSFF682Z-SDEPb80DqRXA0A%3BFUbZRQMdjrHq_ylB9j7ef2Z-SDG_xz_36u8R2Q&oq=Avon+Street&gl=uk&dirflg=w&mra=ltm&t=m&z=15
Whoops – I mean 1910s!