Varying with the Bank 's unbroken increase in height , to , above mean high water , the size of the flint and chert shingle varies from pea-sized at the north-west end ( by West Bay ) to orange-sized at the south-east end ( by Portland ) .
The lagoon is 9 1/2 feet ( 3m ) at its deepest.p99 Varying with the Bank 's unbroken increase in height , to 14.7 m , above mean high water , the size of the flint and chert shingle varies from pea-sized at the north-west end ( by West Bay ) to orange-sized at the south-east end ( by Portland ) .