Charles Henry Hitchcock,
Popular Science Monthly
(1873)
“ If we transport ourselves in imagination to these ancient shores, we shall see that the animals left their hiding-places and were traversing the soft mud laid bare by the ebbing tide, in search of food. The heat of a tropical sun quickly hardens the mud, so that the returning tide, in bringing a fresh deposit of mud, does not wash away the impressions already made on the lower layer, but carefully covers them over. The imprints have, therefore, become a species of mould into which another muddy fluid is poured, and by hardening is made to copy the foot-mark like a plaster cast. ”

