The sage Kashyapa's son was Vivasvana or the sun. The sun was married to Tvashta's (same as Vishvakarma) daughter Samjna. Vivasvana and Samjana had three children, Vaivasvata, Yama and Yamuna. Samjna could not however stand the strong energy of her husband, the sun. From her own body she created Chhaya, a woman who looked just like her. Samjna and Chhaya could not be distinguished from each other.
Samjna told Chhaya, Stay here and retend to be Samjna. Look after my three children, Vaivasvata, Yama and Yamuna. I am going off to my father's house. Don't tell anyone that you are not Samjna. I will do your bidding, replied Chhaya, But the moment someone grasps me by the hair, I will dvulge the truth.
Samjna went to Tvashta's house. When she had spent quite some time there, her father got suspicious and wanted to know why she was not returning to her husband. Samjna therefore adopted the form of a mare and began to live in the kingdom that is known as Uttarakuru.
Meanwhile, the sun and Chhaya had a son named Savarni. It was clear that Chhaya doted on Savarni. In comparison, Yama felt neglected. Yama was still very young and in a fit of rage, he kicked Chhaya. Chhaya cursed Yama. Yama was very surprised at this, since no mother curses her own son. He went and reported it to the sun. The sun deduced that Chhaya could not be Yama's mother. He grasped Chhaya by the hair and the truth came out.
The sun then went to Tvashta in search of Samjna. It was discovered that Samjna had done all this because she could not bear the energy of her husband. Tvashta chiselled off some of the sun's energy so that his radiance become muted.
Learning that Samjna had adopted the form of a mare, the sun adopted the form of a horse. He went and met his wife. As horse and mare, they had two children. These were the twin gods known as the Ashvinis. They were also called Nasatya and Dasra.
Vaivasvata Manu performed a yajna so as to have a son. From the sacrifice, a daughter Ila was born. Chandra's son Budha married Iia and they had a son named Pururava. This was the origin of the lunar dynasty which started with Pururva.
Later on, Vaivasvata Manu had nine sons. Their names were Ikshvaku, Shivi, Nabhaga, Dhrishnu, Sharyati, Narishyanta, Isha, Karusha and Priyavrata. These sons were the originators of the solar dynasty.
Epilogue
The assembled sages were gratified at Romaharshana having recited for them the Shiva Purana. They worshipped Romaharshana. But, warned Romaharshana, never divulge what I have told you, to those who are disrespectful or to those who do not believe in god.
Repeatly, Shiva himself appears in order to bless his devotees. A person who donates the Shiva Purana, along with gold and a bull, gets to live for ever in Shivaloka.