The grand McLennan Arch is located at the western entrance to Glasgow Green around 1990. The arch was presented to his fellow citizens by Bailie James McLennan MP. The arch is dated MDCCCXCIII (1843).
It has four large Ionic columns and a wide central opening which originally framed a window in the Assembly Rooms, which was demolished around 1890.
Sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains.
Most sandstone is composed of quartz or feldspar, because they are the most resistant minerals to the weathering processes at the Earth's surface. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are yellow, red, grey and brown, with some other sandstones being pink, white, and black.
Cross Bedding
Cross bedding is layering within a sandstone rocks, these are at an angle to the main bedding plane.
Cross bedding forms during deposition on the inclined surfaces of bedforms such as ripples and dunes; it indicates that the depositional environment contained a flowing medium of water or wind.
Graded bedding
A graded bed is a bed characterized by a systematic change in grain or clast size from bottom to top of the bed. This most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones.
Graded beds generally represent depositional environments which decrease in transport energy (rate of flow) as time passes, but these beds can also form during rapid depositional events. They are perhaps best represented in turbidite strata, where they indicate a sudden strong current that deposits heavy, coarse sediments first, with finer ones following as the current weakens. They can also form in terrestrial stream deposits.
Lamination bedding
Lamination is 1a small-scale sequence of fine layers that occurs in sedimentary rocks.
Lamination consists of small differences in the type of sediment that occur throughout the rock. They are caused by cyclic changes in the supply of sediment. These changes can occur in grain size, clay percentage, microfossil content, organic material content or mineral content and often result in pronounced differences in colour between the laminae.
Lamination can occur as parallel structures (parallel lamination) or in different sets that make an angle with each other (cross-lamination). It can occur in many different types of sedimentary rock, from coarse sandstone to fine shales, mudstones or in evaporites.
Please send your answers to the following questions to me via the email or the message centre
Questions
- Describe the colour and texture of the blocks?
- Look at the sandstone, what type of bedding do you see here?
- Are the bedding lines fine or large?
- Please upload a photo of yourself or a personal item with the arch in the background