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2. Blatt H. Middleton G.V. Murray R.C. 1980. Origin of Sedimentary Rocks. 2nd edn. Prentice-Hall, Englewood Cliffs, NJ.
3. Folk R.L. 1968. Petrology of Sedimentary Rocks. Hemphill, Austin, TX.
4. HMRC, 2012. Revenue and Customs Brief 21/12, Aggregates Levy: European General Court judgement. Her Majesty’s Revenue and Customs. http://webarchive.nationalarchives.gov.uk/20140109143644/http://www.hmrc.gov.uk/briefs/excise-duty/brief2112.htm.
5. HMRC, 2013. Revenue and Customs Brief 24 (2013): Exemptions and reliefs contained within the aggregates levy. Her Majesty’s Revenue and Customs. https://www.gov.uk/government/publications/revenue-and-customs-brief-24-2013-exemptions-and-reliefs-contained-within-the-aggregates-levy.