Paste color, temper, and texture are consistent when examined microscopically. Resemblance is very close between oven sherds from the Jamestown and Howland house sites, and between these and a large chip obtained from the Smithsonian's oven purchased in Bideford. Except for a somewhat lower proportion of temper, utensil sherds from various sites are consistent with the oven fragments. The Smithsonian's 19th-century Bideford pan also closely resembles these, except for the proportion of temper, which is somewhat less. Further close resemblance of form exists between the Jamestown and Flushing ovens and those in the Bideford Museum. (Figs. 7, 9.) In 1954 comparative tests were made by Frederick H. Norton, professor of ceramics at Massachusetts Institute of Technology. Jamestown clay was used for a control. Thin sections, made of sherds found at Jamestown, were fired at several temperatures and the results recorded in photomicrographs. Of the gravel-tempered sherd submitted in these tests, Professor Norton commented, "The clay mass looks quite dissimilar from the Jamestown clay." No other identifiable English ware of this period compares with the gravel-tempered pottery, the use of gravel for temper apparently being restricted to North Devon. Gravel is found in red earthenware sherds from Spanish colonial sites and in olive oil jars of Hispanic origin, but both the quality and proportion of temper differs, as do the paste characteristics, so that no possibility exists for confusion between them and the North Devon ware. The North Devon potteries produced gravel-tempered ovens that probably were unique in England. Ceramic ovens were made elsewhere, to be sure; Jewitt describes and illustrates an oven made in Yearsley by the Yorkshire Wedgwoods in 1712, but it is in no way related to the North Devon form. We have mentioned Dr. Pococke's allusion to "earthenware ovens" made in the mid-18th century at Calstock on the Cornish side of the Devonshire border, about 35 miles from Bideford; however, one may suppose that these were the products of diffusion from the North Devon center, if, indeed, they even resembled the North Devon ovens.