Wigan Album

Ron, I've been reading up about bricks, and your brick looks to be a historic hand made waterstruck brick which will have been soft fired. It could have been made before the 1600s too with having no frog. As can be read in the links the excess clay is scraped off the top of the mould, and my initial thought was that the wood scraper had a protrusion on it, however on looking closely the groove in the brick looks to have been done deliberately with a round piece of wood dowel i.e., pencil like, it looks to have been stuck into the left side and lifted slightly before being drawn across to the right, and with you saying the other brick has the same marking then I'm thinking it maybe is the brickmakers personal mark, that which identifies all the bricks he/she has made for pay etc., though I'm only surmising about that. There is some interesting information about bricks in all of the links, even with the third link being to an American website.

https://www.ehow.com/how_6828767_trace-masonry-brick-history.html

https://watlingreclamation.co.uk/product-category/building-materials/bricks-reclaimed-new/handmade-bricks/

https://www.ids-dmv.com/masonry/top-5-ways-to-tell-if-a-brick-is-historic-or-contemporary/

They were showing The Victorian Farm Christmas programme on one of the Freeview channels yesterday, and in the programme they were needing bricks to repair the furnace chimney in the Smithy shop, so decided to make their own using the methods of brickmaking at the time, they handmade the bricks using prepared clay and a mould and two methods of firing the bricks were used a kiln and a clamp, . Here's a link to a website that explains and discusses the efficiency of both a kiln and a clamp. I'd never heard of 'lakh,' and had to look it up, and lakh is a hundred thousand, it's Indian apparently:

https://theconstructor.org/building/building-material/kiln-vs-clamp-burning-bricks/35429/#:~:text=The%20burning%20of%20bricks%20should,are%20discussed%20in%20this%20article.

That looks like a stone sett to me.