Worthington Hooker, Science for the School and Family, part. III, Mineralogy and Geology, New York, Harper & Brothers, 1865, pp. 269-270.

We find now that the larvae or grubs of different species use various materials for their indusia, or covers, some gluing together small bits of wood, others choosing grains of sand, and others still the shells of small mollusks. One of the last is seen in Fig. 162. The animal is in a tube which it has constructed for itself of minut shells, and living, in this, it thrusts its bead and a portion of its body out in search of its food. « It is evident , » says Mr. Eley, an English geologist, «  that the larger of the ancient lakes of Auvergne was inhabited by a species of this family, and that they swarmed in it in a remarkable manner; for their cases, incrusted with a calcareous matter, are see to form there thick layers of limestone- called indusial, from this strang origin- which alternate with the more usual kinds of marl through a thickness of several hundred feet. » These indusial strata are eight or ten feet thick and extend over an area of many square miles. When you are told that one of the cases or tubes contains over a hundred shells, and yen or twelve tubes may be counted in a single cubic inch of rock, you may have some idea of the countless myriads of minute mollusks which must have formerly lived and died in every part of this region, and of the length of time required for the formation of the strata constructed chiefly from their shells.