"I cannot say for sure why foundation deposits were deemed necessary"Looking further into this (and there's a good deal of online resources for this) - the placing of foundation deposits was part of a much larger ritualistic ceremony. Information provided by TourEgypt gives us the full ceremony and how foundation deposits fit into it:
Beginning the Construction
1. "Stretching the Cord", thereby fixing the plan of the building.
2. Purifying the area to be built upon by sprinkling gypsum.
3. Digging the first foundation trench
4. Filling the foundation trench with sand
5. Moulding the first brick or bricks
6. Burying the foundation deposits
7. Initiation of the building work
Completion of Construction
8. Purification of the completed temple
9. Presenting the temple to the deities to whom it is dedicated
10. Offering of sacrifices
Thank you to TourEgypt for the information. Although i linked to their site during the original post - i feel it necessary to post the above-to show that foundation deposits are now less of a mystery to me- now that the above is known.
At a later date i will discuss who discovered the various foundation deposits around Deir el Bahri, when they discovered them, what was included and where they are now. A lot more information gathering is necessary before i am able to do this.