Occasionally the position of the patriarch is slightly altered, as in Fig. 65, from the Catacomb of St. Priscilla; but this is all the 287 variety of treatment of which the artistic genius of the age seemed capable. In the bas reliefs the treatment of this subject exhibits a still greater degree of degradation and constraint, as in the following examples from Christian sarcophagi of the fourth century. [Illustration: Fig. 65.--Noah in the Ark.] Sometimes the figure ludicrously resembles the toy called “Jack in a box,” which resemblance is heightened by the lid being half open and a lock being carved on the front. [Illustration: Fig. 66.--Noah in the Ark.] This rude representation, however, was regarded, in accordance with the exposition of St. Peter,[482] as a symbol of Christian baptism; 288 while the ark was the figure of Christ’s church, in which believers “may so pass the waves of this troublesome world that finally they may come to the land of everlasting life.” The dove and olive branch may further imply, that the weary soul, being justified by faith, found peace with God and entered into endless rest.[483] [Illustration: Fig. 67.--Apamean Medal.] Another favourite subject of the early Christian artists was the sacrifice of Isaac, an appropriate type of the greater sacrifice to be offered up when, in the fulness of the time, God should provide himself a lamb for an offering. From this theme the persecuted Christians doubtless often derived spiritual comfort amid the fiery trials of their faith to which they were exposed. It taught also the duty of self-consecration. “May I, like the youthful Isaac,” says Paulinus, “be offered to God a living sacrifice, and, bearing my wood, follow my Holy Father beneath the cross.”[484] This subject is repeated, with considerable variety of treatment, both in frescoes and in sculpture. In Fig. 68, from the cemetery of St. Priscilla, Isaac is seen bearing the wood for the sacrifice. In Fig. 69, from the Catacomb 289 of Marcellinus, he is already bound, and Abraham has stretched forth his hand to slay his son, while the divinely substituted lamb appears from behind the altar. [Illustration: Fig. 68.--The Sacrifice of Isaac.] [Illustration: Fig. 69.--The Sacrifice of Isaac.] In several examples a hand stretched forth from on high seizes the knife to prevent the consummation of the sacrifice. (See Fig. 107.) It is recorded that Gregory of Nyssa frequently shed tears on reading this pathetic story. Joseph, sold by his brethren and afterward saving them alive, was a striking type of Him who redeemed with his own blood the guilty race 290 which caused his death. It is, therefore, a subject that appears with peculiar propriety among the tombs of the primitive Christians.