On track four of Sierra Hull’s second CD, you can get a pretty good idea why people like Dolly Parton and Alison Krauss think this young woman is pretty hot stuff when it comes to prodigious talent. She plays mandolin like she was born with the instrument in her hand, and on “Bombshell” (an instrumental she wrote), Hull lays down a marker. This is a player to reckon with, despite her youth. She was only 15 when she recorded Secrets, her first album, and now, at the ripe old age of 19, she sings like a bluegrass angel. But, if you didn’t know her age, or hadn’t heard any of the hype that focuses on her youth, you’d surely think this was the work of a mature artist. On “Chasin’ Skies,” another instrumental she wrote, the interplay of mandolin and banjo just about defines the bluegrass tradition, and extends it some, too. She writes good songs; she plays with mastery; she sings with perfect control and real feeling. If Bill Monroe is looking down from that big bluegrass band in the sky, cocking an ear to what mandolin players are producing back on earth these days, he’s going to be smiling at the sounds Hull is sending up.