Some Reef-Building Calcareous Algae From the Carboniferous Rocks of Northern England and Southern Scotland

( Read, February , 1948). The various growth-forms assumed by algal colonies are described and it is suggested that they are determined primarily by environmental factors. A study of the sediments associated with these growth-forms indicates that reef-building algae flourished in shallow, disturbed water, rich in silica and iron. Periods of vulcanicity appear to produce an environment favourable to algal growth. Three main algal phases in the Lower Carboniferous rocks of northern England and southern Scotland are described,—the main Algal Series of C1, the Burdiehouse Limestone horizon in S1 and the Girvanella -bearing limestones at the top of D1. A number of new growth-forms are described. According to Pia’s classification of the fossil algae ( in Hirmer, 1927) the group Spongiostromata includes the more massive reef-building forms such as Weedia Walcott, Collenia Walcott, Cryptozoon Hall, Archaeozoon Matthew, Gymnosolen Steinmann, Pycnostroma Gurich, Wingia Seely, Osagia Twenhofel, Ottonosia Twenhofel and Spongiostroma Gurich. With the exception of Spongiostroma these generic names refer to a variety of growth forms, which, it is suggested, represent the remains of algal colonies. When Pia’s account was published none of these, with the possible exception of Cryptozoon , could be demonstrated to possess any undoubted algal structures such as are seen in the similar, but more recent, Corallinaceae (e.g. Lithothamnium ). The recent work of Johnson (1946), however, has shown that some of these growth-forms represent the shapes assumed by the aggregate of a number of algal filaments not always all of the same kind, which suggests that they are the remains of ...